Topswops
Topswops is a card game created by John Conway in the 1970's.
You are encouraged to solve this task according to the task description, using any language you may know.
Assume you have a particular permutation of a set of n cards numbered 1..n on both of their faces, for example the arrangement of four cards given by [2, 4, 1, 3] where the leftmost card is on top.
A round is composed of reversing the first m cards where m is the value of the topmost card.
Rounds are repeated until the topmost card is the number 1 and the number of swaps is recorded.
For our example the swaps produce:
[2, 4, 1, 3] # Initial shuffle [4, 2, 1, 3] [3, 1, 2, 4] [2, 1, 3, 4] [1, 2, 3, 4]
For a total of four swaps from the initial ordering to produce the terminating case where 1 is on top.
For a particular number n
of cards, topswops(n)
is the maximum swaps needed for any starting permutation of the n
cards.
- Task
The task is to generate and show here a table of n
vs topswops(n)
for n
in the range 1..10 inclusive.
- Note
Topswops is also known as Fannkuch from the German Pfannkuchen meaning pancake.
- Related tasks
360 Assembly
The program uses two ASSIST macro (XDECO,XPRNT) to keep the code as short as possible. <lang 360asm>* Topswops optimized 12/07/2016 TOPSWOPS CSECT
USING TOPSWOPS,R13 base register B 72(R15) skip savearea DC 17F'0' savearea STM R14,R12,12(R13) prolog ST R13,4(R15) " <- ST R15,8(R13) " -> LR R13,R15 " addressability MVC N,=F'1' n=1
LOOPN L R4,N n; do n=1 to 10 ===-------------==*
C R4,=F'10' " * BH ELOOPN . * MVC P(40),PINIT p=pinit MVC COUNTM,=F'0' countm=0
REPEAT MVC CARDS(40),P cards=p -------------------------+
SR R11,R11 count=0 |
WHILE CLC CARDS,=F'1' do while cards(1)^=1 ---------+
BE EWHILE . | MVC M,CARDS m=cards(1) L R2,M m SRA R2,1 m/2 ST R2,MD2 md2=m/2 L R3,M @card(mm)=m SLA R3,2 *4 LA R3,CARDS-4(R3) @card(mm) LA R2,CARDS @card(i)=0 LA R6,1 i=1
LOOPI C R6,MD2 do i=1 to m/2 -------------+
BH ELOOPI . | L R0,0(R2) swap r0=cards(i) MVC 0(4,R2),0(R3) swap cards(i)=cards(mm) ST R0,0(R3) swap cards(mm)=r0 AH R2,=H'4' @card(i)=@card(i)+4 SH R3,=H'4' @card(mm)=@card(mm)-4 LA R6,1(R6) i=i+1 | B LOOPI ----------------------------+
ELOOPI LA R11,1(R11) count=count+1 |
B WHILE -------------------------------+
EWHILE C R11,COUNTM if count>countm
BNH NOTGT then ST R11,COUNTM countm=count
NOTGT BAL R14,NEXTPERM call nextperm
LTR R0,R0 until nextperm=0 | BNZ REPEAT ---------------------------------+ L R1,N n XDECO R1,XDEC edit n MVC PG(2),XDEC+10 output n MVI PG+2,C':' output ':' L R1,COUNTM countm XDECO R1,XDEC edit countm MVC PG+3(4),XDEC+8 output countm XPRNT PG,L'PG print buffer L R1,N n * LA R1,1(R1) +1 * ST R1,N n=n+1 * B LOOPN ===------------------------------==*
ELOOPN L R13,4(0,R13) epilog
LM R14,R12,12(R13) " restore XR R15,R15 " rc=0 BR R14 exit
PINIT DC F'1',F'2',F'3',F'4',F'5',F'6',F'7',F'8',F'9',F'10' CARDS DS 10F cards P DS 10F p COUNTM DS F countm M DS F m N DS F n MD2 DS F m/2 PG DC CL20' ' buffer XDEC DS CL12 temp
- ------- ---- nextperm ----------{-----------------------------------
NEXTPERM L R9,N nn=n
SR R8,R8 jj=0 LR R7,R9 nn BCTR R7,0 j=nn-1 LTR R7,R7 if j=0 BZ ELOOPJ1 then skip do loop
LOOPJ1 LR R1,R7 do j=nn-1 to 1 by -1; j ----+
SLA R1,2 . | L R2,P-4(R1) p(j) C R2,P(R1) if p(j)<p(j+1) BNL PJGEPJP then LR R8,R7 jj=j B ELOOPJ1 leave j |
PJGEPJP BCT R7,LOOPJ1 j=j-1 ---------------------+ ELOOPJ1 LA R7,1(R8) j=jj+1 LOOPJ2 CR R7,R9 do j=jj+1 while j<nn ------+
BNL ELOOPJ2 . | LR R2,R7 j SLA R2,2 . LR R3,R9 nn SLA R3,2 . L R0,P-4(R2) swap p(j),p(nn) L R1,P-4(R3) " ST R0,P-4(R3) " ST R1,P-4(R2) " BCTR R9,0 nn=nn-1 LA R7,1(R7) j=j+1 | B LOOPJ2 ----------------------------+
ELOOPJ2 LTR R8,R8 if jj=0
BNZ JJNE0 then LA R0,0 return(0) BR R14 "
JJNE0 LA R7,1(R8) j=jj+1
LR R2,R7 j SLA R2,2 r@p(j) LR R3,R8 jj SLA R3,2 r@p(jj)
LOOPJ3 L R0,P-4(R2) p(j) ----------------------+
C R0,P-4(R3) do j=jj+1 while p(j)<p(jj) | BNL ELOOPJ3 LA R2,4(R2) r@p(j)=r@p(j)+4 LA R7,1(R7) j=j+1 | B LOOPJ3 ----------------------------+
ELOOPJ3 L R1,P-4(R3) swap p(j),p(jj)
ST R0,P-4(R3) " ST R1,P-4(R2) " LA R0,1 return(1) BR R14 ---------------}----------------------------------- YREGS END TOPSWOPS</lang>
- Output:
1: 0 2: 1 3: 2 4: 4 5: 7 6: 10 7: 16 8: 22 9: 30 10: 38
Ada
This is a straightforward approach that counts the number of swaps for each permutation. To generate all permutations over 1 .. N, for each of N in 1 .. 10, the package Generic_Perm from the Permutations task is used [[1]].
<lang Ada>with Ada.Integer_Text_IO, Generic_Perm;
procedure Topswaps is
function Topswaps(Size: Positive) return Natural is package Perms is new Generic_Perm(Size); P: Perms.Permutation; Done: Boolean; Max: Natural; function Swapper_Calls(P: Perms.Permutation) return Natural is
Q: Perms.Permutation := P; I: Perms.Element := P(1);
begin
if I = 1 then return 0; else for Idx in 1 .. I loop Q(Idx) := P(I-Idx+1); end loop; return 1 + Swapper_Calls(Q); end if;
end Swapper_Calls; begin Perms.Set_To_First(P, Done); Max:= Swapper_Calls(P); while not Done loop
Perms.Go_To_Next(P, Done); Max := natural'Max(Max, Swapper_Calls(P));
end loop; return Max; end Topswaps;
begin
for I in 1 .. 10 loop Ada.Integer_Text_IO.Put(Item => Topswaps(I), Width => 3); end loop;
end Topswaps;</lang>
- Output:
0 1 2 4 7 10 16 22 30 38
AutoHotkey
<lang AutoHotkey>Topswops(Obj, n){ R := [] for i, val in obj{ if (i <=n) res := val (A_Index=1?"":",") res else res .= "," val } Loop, Parse, res, `, R[A_Index]:= A_LoopField return R }</lang> Examples:<lang AutoHotkey>Cards := [2, 4, 1, 3] Res := Print(Cards) while (Cards[1]<>1) { Cards := Topswops(Cards, Cards[1]) Res .= "`n"Print(Cards) } MsgBox % Res
Print(M){ for i, val in M Res .= (A_Index=1?"":"`t") val return Trim(Res,"`n") }</lang>
Outputs:
2 4 1 3 4 2 1 3 3 1 2 4 2 1 3 4 1 2 3 4
C
An algorithm that doesn't go through all permutations, per Knuth tAoCP 7.2.1.2 exercise 107 (possible bad implementation on my part notwithstanding): <lang c>#include <stdio.h>
- include <string.h>
typedef struct { char v[16]; } deck; typedef unsigned int uint;
uint n, d, best[16];
void tryswaps(deck *a, uint f, uint s) {
- define A a->v
- define B b.v
if (d > best[n]) best[n] = d; while (1) { if ((A[s] == s || (A[s] == -1 && !(f & 1U << s))) && (d + best[s] >= best[n] || A[s] == -1)) break;
if (d + best[s] <= best[n]) return; if (!--s) return; }
d++; deck b = *a; for (uint i = 1, k = 2; i <= s; k <<= 1, i++) { if (A[i] != i && (A[i] != -1 || (f & k))) continue;
for (uint j = B[0] = i; j--;) B[i - j] = A[j]; tryswaps(&b, f | k, s); } d--; }
int main(void) { deck x; memset(&x, -1, sizeof(x)); x.v[0] = 0;
for (n = 1; n < 13; n++) { tryswaps(&x, 1, n - 1); printf("%2d: %d\n", n, best[n]); }
return 0; }</lang> The code contains critical small loops, which can be manually unrolled for those with OCD. POSIX thread support is useful if you got more than one CPUs. <lang c>#define _GNU_SOURCE
- include <stdio.h>
- include <string.h>
- include <pthread.h>
- include <sched.h>
- define MAX_CPUS 8 // increase this if you got more CPUs/cores
typedef struct { char v[16]; } deck;
int n, best[16];
// Update a shared variable by spinlock. Since this program really only // enters locks dozens of times, a pthread_mutex_lock() would work // equally fine, but RC already has plenty of examples for that.
- define SWAP_OR_RETRY(var, old, new) \
if (!__sync_bool_compare_and_swap(&(var), old, new)) { \ volatile int spin = 64; \ while (spin--); \ continue; }
void tryswaps(deck *a, int f, int s, int d) {
- define A a->v
- define B b->v
while (best[n] < d) { int t = best[n]; SWAP_OR_RETRY(best[n], t, d); }
- define TEST(x) \
case x: if ((A[15-x] == 15-x || (A[15-x] == -1 && !(f & 1<<(15-x)))) \ && (A[15-x] == -1 || d + best[15-x] >= best[n])) \ break; \ if (d + best[15-x] <= best[n]) return; \ s = 14 - x
switch (15 - s) { TEST(0); TEST(1); TEST(2); TEST(3); TEST(4); TEST(5); TEST(6); TEST(7); TEST(8); TEST(9); TEST(10); TEST(11); TEST(12); TEST(13); TEST(14); return; }
- undef TEST
deck *b = a + 1; *b = *a; d++;
- define FLIP(x) \
if (A[x] == x || ((A[x] == -1) && !(f & (1<<x)))) { \ B[0] = x; \ for (int j = x; j--; ) B[x-j] = A[j]; \ tryswaps(b, f|(1<<x), s, d); } \ if (s == x) return;
FLIP(1); FLIP(2); FLIP(3); FLIP(4); FLIP(5); FLIP(6); FLIP(7); FLIP(8); FLIP(9); FLIP(10); FLIP(11); FLIP(12); FLIP(13); FLIP(14); FLIP(15);
- undef FLIP
}
int num_cpus(void) { cpu_set_t ct; sched_getaffinity(0, sizeof(ct), &ct);
int cnt = 0; for (int i = 0; i < MAX_CPUS; i++) if (CPU_ISSET(i, &ct)) cnt++;
return cnt; }
struct work { int id; deck x[256]; } jobs[MAX_CPUS]; int first_swap;
void *thread_start(void *arg) { struct work *job = arg; while (1) { int at = first_swap; if (at >= n) return 0;
SWAP_OR_RETRY(first_swap, at, at + 1);
memset(job->x, -1, sizeof(deck)); job->x[0].v[at] = 0; job->x[0].v[0] = at; tryswaps(job->x, 1 | (1 << at), n - 1, 1); } }
int main(void) { int n_cpus = num_cpus();
for (int i = 0; i < MAX_CPUS; i++) jobs[i].id = i;
pthread_t tid[MAX_CPUS];
for (n = 2; n <= 14; n++) { int top = n_cpus; if (top > n) top = n;
first_swap = 1; for (int i = 0; i < top; i++) pthread_create(tid + i, 0, thread_start, jobs + i);
for (int i = 0; i < top; i++) pthread_join(tid[i], 0);
printf("%2d: %2d\n", n, best[n]); }
return 0; }</lang>
C++
<lang cpp>/*
Author: Kevin Bacon [haxifix (@gmail.com)] Date: 2018-05-16
- /
- include <iostream>
- include <vector>
- include <numeric>
- include <algorithm>
int topswops(int n) {
std::vector<int> list(n); std::iota(std::begin(list), std::end(list), 1); int max_steps = 0; do { auto temp_list = list; for (int steps = 1; temp_list[0] != 1; ++steps) { std::reverse(std::begin(temp_list), std::begin(temp_list) + temp_list[0]); if (steps > max_steps) max_steps = steps; } } while (std::next_permutation(std::begin(list), std::end(list))); return max_steps;
}
int main() {
for (int i = 1; i <= 10; ++i) { std::cout << i << ": " << topswops(i) << std::endl; } return 0;
}</lang>
- Output:
1: 0 2: 1 3: 2 4: 4 5: 7 6: 10 7: 16 8: 22 9: 30 10: 38
D
Permutations generator from: http://rosettacode.org/wiki/Permutations#Faster_Lazy_Version
<lang d>import std.stdio, std.algorithm, std.range, permutations2;
int topswops(in int n) pure @safe {
static int flip(int[] xa) pure nothrow @safe @nogc { if (!xa[0]) return 0; xa[0 .. xa[0] + 1].reverse(); return 1 + flip(xa); } return n.iota.array.permutations.map!flip.reduce!max;
}
void main() {
foreach (immutable i; 1 .. 11) writeln(i, ": ", i.topswops);
}</lang>
- Output:
1: 0 2: 1 3: 2 4: 4 5: 7 6: 10 7: 16 8: 22 9: 30 10: 38
D: Faster Version
<lang d>import std.stdio, std.typecons;
__gshared uint[32] best;
uint topswops(size_t n)() nothrow @nogc {
static assert(n > 0 && n < best.length); size_t d = 0;
alias T = byte; alias Deck = T[n];
void trySwaps(in ref Deck deck, in uint f) nothrow @nogc { if (d > best[n]) best[n] = d;
foreach_reverse (immutable i; staticIota!(0, n)) { if ((deck[i] == i || (deck[i] == -1 && !(f & (1U << i)))) && (d + best[i] >= best[n] || deck[i] == -1)) break; if (d + best[i] <= best[n]) return; }
Deck deck2 = void; foreach (immutable i; staticIota!(0, n)) // Copy. deck2[i] = deck[i];
d++; foreach (immutable i; staticIota!(1, n)) { enum uint k = 1U << i; if (deck[i] != i && (deck[i] != -1 || (f & k))) continue;
deck2[0] = T(i); foreach_reverse (immutable j; staticIota!(0, i)) deck2[i - j] = deck[j]; // Reverse copy. trySwaps(deck2, f | k); } d--; }
best[n] = 0; Deck deck0 = -1; deck0[0] = 0; trySwaps(deck0, 1); return best[n];
}
void main() {
foreach (immutable i; staticIota!(1, 14)) writefln("%2d: %d", i, topswops!i());
}</lang>
- Output:
1: 0 2: 1 3: 2 4: 4 5: 7 6: 10 7: 16 8: 22 9: 30 10: 38 11: 51 12: 65 13: 80
With templates to speed up the computation, using the DMD compiler it's almost as fast as the second C version.
Eiffel
<lang Eiffel> class TOPSWOPS
create make
feature
make (n: INTEGER) -- Topswop game. local perm, ar: ARRAY [INTEGER] tcount, count: INTEGER do create perm_sol.make_empty create solution.make_empty across 1 |..| n as c loop create ar.make_filled (0, 1, c.item) across 1 |..| c.item as d loop ar [d.item] := d.item end permute (ar, 1) across 1 |..| perm_sol.count as e loop tcount := 0 from until perm_sol.at (e.item).at (1) = 1 loop perm_sol.at (e.item) := reverse_array (perm_sol.at (e.item)) tcount := tcount + 1 end if tcount > count then count := tcount end end solution.force (count, c.item) end end
solution: ARRAY [INTEGER]
feature {NONE}
perm_sol: ARRAY [ARRAY [INTEGER]]
reverse_array (ar: ARRAY [INTEGER]): ARRAY [INTEGER] -- Array with 'ar[1]' elements reversed. require ar_not_void: ar /= Void local i, j: INTEGER do create Result.make_empty Result.deep_copy (ar) from i := 1 j := ar [1] until i > j loop Result [i] := ar [j] Result [j] := ar [i] i := i + 1 j := j - 1 end ensure same_elements: across ar as a all Result.has (a.item) end end
permute (a: ARRAY [INTEGER]; k: INTEGER) -- All permutations of array 'a' stored in perm_sol. require ar_not_void: a.count >= 1 k_valid_index: k > 0 local i, t: INTEGER temp: ARRAY [INTEGER] do create temp.make_empty if k = a.count then across a as ar loop temp.force (ar.item, temp.count + 1) end perm_sol.force (temp, perm_sol.count + 1) else from i := k until i > a.count loop t := a [k] a [k] := a [i] a [i] := t permute (a, k + 1) t := a [k] a [k] := a [i] a [i] := t i := i + 1 end end end
end </lang> Test: <lang Eiffel> class APPLICATION
create make
feature
make do create topswop.make (10) across topswop.solution as t loop io.put_string (t.item.out + "%N") end end
topswop: TOPSWOPS
end </lang>
- Output:
0 1 2 4 7 10 16 22 30 38
Elixir
<lang elixir>defmodule Topswops do
def get_1_first( [1 | _t] ), do: 0 def get_1_first( list ), do: 1 + get_1_first( swap(list) ) defp swap( [n | _t]=list ) do {swaps, remains} = Enum.split( list, n ) Enum.reverse( swaps, remains ) end def task do IO.puts "N\ttopswaps" Enum.map(1..10, fn n -> {n, permute(Enum.to_list(1..n))} end) |> Enum.map(fn {n, n_permutations} -> {n, get_1_first_many(n_permutations)} end) |> Enum.map(fn {n, n_swops} -> {n, Enum.max(n_swops)} end) |> Enum.each(fn {n, max} -> IO.puts "#{n}\t#{max}" end) end def get_1_first_many( n_permutations ), do: (for x <- n_permutations, do: get_1_first(x)) defp permute([]), do: [[]] defp permute(list), do: for x <- list, y <- permute(list -- [x]), do: [x|y]
end
Topswops.task</lang>
- Output:
N topswaps 1 0 2 1 3 2 4 4 5 7 6 10 7 16 8 22 9 30 10 38
Erlang
This code is using the permutation code by someone else. Thank you. <lang Erlang> -module( topswops ).
-export( [get_1_first/1, swap/1, task/0] ).
get_1_first( [1 | _T] ) -> 0; get_1_first( List ) -> 1 + get_1_first( swap(List) ).
swap( [N | _T]=List ) -> {Swaps, Remains} = lists:split( N, List ), lists:reverse( Swaps ) ++ Remains.
task() -> Permutations = [{X, permute:permute(lists:seq(1, X))} || X <- lists:seq(1, 10)], Swops = [{N, get_1_first_many(N_permutations)} || {N, N_permutations} <- Permutations], Topswops = [{N, lists:max(N_swops)} || {N, N_swops} <- Swops], io:fwrite( "N topswaps~n" ), [io:fwrite("~p ~p~n", [N, Max]) || {N, Max} <- Topswops].
get_1_first_many( N_permutations ) -> [get_1_first(X) || X <- N_permutations]. </lang>
- Output:
42> topswops:task(). N topswaps 1 0 2 1 3 2 4 4 5 7 6 10 7 16 8 22 9 30 10 38
Fortran
<lang Fortran>module top implicit none contains recursive function f(x) result(m)
integer :: n, m, x(:),y(size(x)), fst fst = x(1) if (fst == 1) then m = 0 else y(1:fst) = x(fst:1:-1) y(fst+1:) = x(fst+1:) m = 1 + f(y) end if
end function
recursive function perms(x) result(p) integer, pointer :: p(:,:), q(:,:) integer :: x(:), n, k, i n = size(x) if (n == 1) then
allocate(p(1,1)) p(1,:) = x
else
q => perms(x(2:n)) k = ubound(q,1) allocate(p(k*n,n)) p = 0 do i = 1,n p(1+k*(i-1):k*i,1:i-1) = q(:,1:i-1) p(1+k*(i-1):k*i,i) = x(1) p(1+k*(i-1):k*i,i+1:) = q(:,i:) end do
end if end function end module
program topswort use top implicit none integer :: x(10) integer, pointer :: p(:,:) integer :: i, j, m
forall(i=1:10)
x(i) = i
end forall
do i = 1,10
p=>perms(x(1:i)) m = 0 do j = 1, ubound(p,1) m = max(m, f(p(j,:))) end do print "(i3,a,i3)", i,": ",m
end do end program </lang>
Go
<lang go>// Adapted from http://www-cs-faculty.stanford.edu/~uno/programs/topswops.w // at Donald Knuth's web site. Algorithm credited there to Pepperdine // and referenced to Mathematical Gazette 73 (1989), 131-133. package main
import "fmt"
const ( // array sizes
maxn = 10 // max number of cards maxl = 50 // upper bound for number of steps
)
func main() {
for i := 1; i <= maxn; i++ { fmt.Printf("%d: %d\n", i, steps(i)) }
}
func steps(n int) int {
var a, b [maxl][maxn + 1]int var x [maxl]int a[0][0] = 1 var m int for l := 0; ; { x[l]++ k := int(x[l]) if k >= n { if l <= 0 { break } l-- continue } if a[l][k] == 0 { if b[l][k+1] != 0 { continue } } else if a[l][k] != k+1 { continue } a[l+1] = a[l] for j := 1; j <= k; j++ { a[l+1][j] = a[l][k-j] } b[l+1] = b[l] a[l+1][0] = k + 1 b[l+1][k+1] = 1 if l > m-1 { m = l + 1 } l++ x[l] = 0 } return m
}</lang>
- Output:
1: 0 2: 1 3: 2 4: 4 5: 7 6: 10 7: 16 8: 22 9: 30 10: 38
Haskell
Searching permutations
<lang Haskell>import Data.List (permutations)
topswops :: Int -> Int topswops n = maximum $ map tops $ permutations [1 .. n]
where tops (1 : _) = 0 tops xa@(x : _) = 1 + tops reordered where reordered = reverse (take x xa) ++ drop x xa
main = mapM_
(\x -> putStrLn $ show x ++ ":\t" ++ show (topswops x)) [1 .. 10]</lang>
- Output:
1: 0 2: 1 3: 2 4: 4 5: 7 6: 10 7: 16 8: 22 9: 30 10: 38
Searching derangements
Alternate version
Uses only permutations with all elements out of place.
<lang Haskell>import Data.List (permutations, inits)
import Control.Arrow (first)
derangements :: [Int] -> Int derangements = (filter . (and .) . zipWith (/=)) <*> permutations
topswop :: Int -> [a] -> [a] topswop = ((uncurry (++) . first reverse) .) . splitAt
topswopIter :: [Int] -> Int topswopIter = takeWhile ((/= 1) . head) . iterate (topswop =<< head)
swops :: [Int] -> [Int] swops = fmap (length . topswopIter) . derangements
topSwops :: [Int] -> [(Int, Int)] topSwops = zip [1 ..] . fmap (maximum . (0 :) . swops) . tail . inits
main :: IO () main = mapM_ print $ take 10 $ topSwops [1 ..]</lang> Output
*Main> mapM_ print $ take 10 $ topSwops [1..] (1,0) (2,1) (3,2) (4,4) (5,7) (6,10) (7,16) (8,22) (9,30) (10,38)
Icon and Unicon
This doesn't compile in Icon only because of the use of list comprehension to build the original list of 1..n values.
<lang unicon>procedure main()
every n := 1 to 10 do { ts := 0 every (ts := 0) <:= swop(permute([: 1 to n :])) write(right(n, 3),": ",right(ts,4)) }
end
procedure swop(A)
count := 0 while A[1] ~= 1 do { A := reverse(A[1+:A[1]]) ||| A[(A[1]+1):0] count +:= 1 } return count
end
procedure permute(A)
if *A <= 1 then return A suspend [(A[1]<->A[i := 1 to *A])] ||| permute(A[2:0])
end</lang>
Sample run:
->topswop 1: 0 2: 1 3: 2 4: 4 5: 7 6: 10 7: 16 8: 22 9: 30 10: 38 ->
J
Solution:<lang j> swops =: ((|.@:{. , }.)~ {.)^:a:</lang> Example (from task introduction):<lang j> swops 2 4 1 3 2 4 1 3 4 2 1 3 3 1 2 4 2 1 3 4 1 2 3 4</lang> Example (topswops of all permutations of the integers 1..10):<lang j> (,. _1 + ! >./@:(#@swops@A. >:)&i. ])&> 1+i.10
1 0 2 1 3 2 4 4 5 7 6 10 7 16 8 22 9 30
10 38</lang> Notes: Readers less familiar with array-oriented programming may find an alternate solution written in the structured programming style more accessible.
Java
<lang java>public class Topswops {
static final int maxBest = 32; static int[] best;
static private void trySwaps(int[] deck, int f, int d, int n) { if (d > best[n]) best[n] = d;
for (int i = n - 1; i >= 0; i--) { if (deck[i] == -1 || deck[i] == i) break; if (d + best[i] <= best[n]) return; }
int[] deck2 = deck.clone(); for (int i = 1; i < n; i++) { final int k = 1 << i; if (deck2[i] == -1) { if ((f & k) != 0) continue; } else if (deck2[i] != i) continue;
deck2[0] = i; for (int j = i - 1; j >= 0; j--) deck2[i - j] = deck[j]; // Reverse copy. trySwaps(deck2, f | k, d + 1, n); } }
static int topswops(int n) { assert(n > 0 && n < maxBest); best[n] = 0; int[] deck0 = new int[n + 1]; for (int i = 1; i < n; i++) deck0[i] = -1; trySwaps(deck0, 1, 0, n); return best[n]; }
public static void main(String[] args) { best = new int[maxBest]; for (int i = 1; i < 11; i++) System.out.println(i + ": " + topswops(i)); }
}</lang>
- Output:
1: 0 2: 1 3: 2 4: 4 5: 7 6: 10 7: 16 8: 22 9: 30 10: 38
jq
The following uses permutations and is therefore impractical for n>10 or so.
Infrastructure: <lang jq># "while" as defined here is included in recent versions (>1.4) of jq: def until(cond; next):
def _until: if cond then . else (next|_until) end; _until;
- Generate a stream of permutations of [1, ... n].
- This implementation uses arity-0 filters for speed.
def permutations:
# Given a single array, insert generates a stream by inserting (length+1) at different positions def insert: # state: [m, array] .[0] as $m | (1+(.[1]|length)) as $n | .[1] | if $m >= 0 then (.[0:$m] + [$n] + .[$m:]), ([$m-1, .] | insert) else empty end;
if .==0 then [] elif . == 1 then [1] else . as $n | ($n-1) | permutations | [$n-1, .] | insert end;</lang>
Topswops: <lang jq># Input: a permutation; output: an integer def flips:
# state: [i, array] [0, .] | until( .[1][0] == 1; .[1] as $p | $p[0] as $p0
| [.[0] + 1, ($p[:$p0] | reverse) + $p[$p0:] ] )
| .[0];
- input: n, the number of items
def fannkuch:
reduce permutations as $p (0; [., ($p|flips) ] | max);</lang>
Example: <lang jq>range(1; 11) | [., fannkuch ]</lang>
- Output:
<lang sh>$ jq -n -c -f topswops.jq [1,0] [2,1] [3,2] [4,4] [5,7] [6,10] [7,16] [8,22] [9,30] [10,38]</lang>
Julia
Fast, efficient version <lang julia>function fannkuch(n) n == 1 && return 0 n == 2 && return 1 p = [1:n] q = copy(p) s = copy(p) sign = 1; maxflips = sum = 0 while true q0 = p[1] if q0 != 1 for i = 2:n q[i] = p[i] end flips = 1 while true qq = q[q0] #?? if qq == 1 sum += sign*flips flips > maxflips && (maxflips = flips) break end q[q0] = q0 if q0 >= 4 i = 2; j = q0-1 while true t = q[i] q[i] = q[j] q[j] = t i += 1 j -= 1 i >= j && break end end q0 = qq flips += 1 end end #permute if sign == 1 t = p[2] p[2] = p[1] p[1] = t sign = -1 else t = p[2] p[2] = p[3] p[3] = t sign = 1 for i = 3:n sx = s[i] if sx != 1 s[i] = sx-1 break end i == n && return maxflips s[i] = i t = p[1] for j = 1:i p[j] = p[j+1] end p[i+1] = t end end end end</lang>
- Output:
julia> function main() for i = 1:10 println(fannkuch(i)) end end # methods for generic function main main() at none:2 julia> @time main() 0 1 2 4 7 10 16 22 30 38 elapsed time: 0.299617582 seconds
Kotlin
<lang scala>// version 1.1.2
val best = IntArray(32)
fun trySwaps(deck: IntArray, f: Int, d: Int, n: Int) {
if (d > best[n]) best[n] = d for (i in n - 1 downTo 0) { if (deck[i] == -1 || deck[i] == i) break if (d + best[i] <= best[n]) return } val deck2 = deck.copyOf() for (i in 1 until n) { val k = 1 shl i if (deck2[i] == -1) { if ((f and k) != 0) continue } else if (deck2[i] != i) continue deck2[0] = i for (j in i - 1 downTo 0) deck2[i - j] = deck[j] trySwaps(deck2, f or k, d + 1, n) }
}
fun topswops(n: Int): Int {
require(n > 0 && n < best.size) best[n] = 0 val deck0 = IntArray(n + 1) for (i in 1 until n) deck0[i] = -1 trySwaps(deck0, 1, 0, n) return best[n]
}
fun main(args: Array<String>) {
for (i in 1..10) println("${"%2d".format(i)} : ${topswops(i)}")
}</lang>
- Output:
1 : 0 2 : 1 3 : 2 4 : 4 5 : 7 6 : 10 7 : 16 8 : 22 9 : 30 10 : 38
Lua
<lang Lua>-- Return an iterator to produce every permutation of list function permute (list)
local function perm (list, n) if n == 0 then coroutine.yield(list) end for i = 1, n do list[i], list[n] = list[n], list[i] perm(list, n - 1) list[i], list[n] = list[n], list[i] end end return coroutine.wrap(function() perm(list, #list) end)
end
-- Perform one topswop round on table t function swap (t)
local new, limit = {}, t[1] for i = 1, #t do if i <= limit then new[i] = t[limit - i + 1] else new[i] = t[i] end end return new
end
-- Find the most swaps needed for any starting permutation of n cards function topswops (n)
local numTab, highest, count = {}, 0 for i = 1, n do numTab[i] = i end for numList in permute(numTab) do count = 0 while numList[1] ~= 1 do numList = swap(numList) count = count + 1 end if count > highest then highest = count end end return highest
end
-- Main procedure for i = 1, 10 do print(i, topswops(i)) end</lang>
- Output:
1 0 2 1 3 2 4 4 5 7 6 10 7 16 8 22 9 30 10 38
Mathematica
An exhaustive search of all possible permutations is done <lang Mathematica>flip[a_] :=
Block[{a1 = First@a}, If[a1 == Length@a, Reverse[a], Join[Reverse[a;; a1], aa1 + 1 ;;]]]
swaps[a_] := Length@FixedPointList[flip, a] - 2
Print[#, ": ", Max[swaps /@ Permutations[Range@#]]] & /@ Range[10];</lang>
- Output:
1: 0 2: 1 3: 2 4: 4 5: 7 6: 10 7: 16 8: 22 9: 30 10: 38
PARI/GP
Naive solution: <lang parigp>flip(v:vec)={
my(t=v[1]+1); if (t==2, return(0)); for(i=1,t\2, [v[t-i],v[i]]=[v[i],v[t-i]]); 1+flip(v)
} topswops(n)={
my(mx); for(i=0,n!-1, mx=max(flip(Vecsmall(numtoperm(n,i))),mx) ); mx;
} vector(10,n,topswops(n))</lang>
- Output:
%1 = [0, 1, 2, 4, 7, 10, 16, 22, 30, 38]
An efficient solution would use PARI, following the C solution.
Perl
Recursive backtracking solution, starting with the final state and going backwards. <lang perl> sub next_swop {
my( $max, $level, $p, $d ) = @_; my $swopped = 0; for( 2..@$p ){ # find possibilities my @now = @$p; if( $_ == $now[$_-1] ) { splice @now, 0, 0, reverse splice @now, 0, $_; $swopped = 1; next_swop( $max, $level+1, \@now, [ @$d ] ); } } for( 1..@$d ) { # create possibilities my @now = @$p; my $next = shift @$d; if( not $now[$next-1] ) { $now[$next-1] = $next; splice @now, 0, 0, reverse splice @now, 0, $next; $swopped = 1; next_swop( $max, $level+1, \@now, [ @$d ] ); } push @$d, $next; } $$max = $level if !$swopped and $level > $$max;
}
sub topswops {
my $n = shift; my @d = 2..$n; my @p = ( 1, (0) x ($n-1) ); my $max = 0; next_swop( \$max, 0, \@p, \@d ); return $max;
}
printf "Maximum swops for %2d cards: %2d\n", $_, topswops $_ for 1..10; </lang>
- Output:
Maximum swops for 1 cards: 0 Maximum swops for 2 cards: 1 Maximum swops for 3 cards: 2 Maximum swops for 4 cards: 4 Maximum swops for 5 cards: 7 Maximum swops for 6 cards: 10 Maximum swops for 7 cards: 16 Maximum swops for 8 cards: 22 Maximum swops for 9 cards: 30 Maximum swops for 10 cards: 38
Perl 6
<lang perl6>sub swops(@a is copy) {
my $count = 0; until @a[0] == 1 { @a[ ^@a[0] ] .= reverse; $count++; } return $count;
}
sub topswops($n) { (sort map &swops, (1..$n).permutations)[*-1] }
say "$_ {topswops $_}" for 1 .. 10;</lang>
Output follows that of Python.
Phix
Originally contributed by Jason Gade as part of the Euphoria version of the Great Computer Language Shootout benchmarks. <lang Phix>function fannkuch(integer n) sequence start = tagset(n),
perm, perm1 = start, count = start
integer maxFlipsCount = 0, r = n+1 integer perm0, flipsCount, k, k2, j, j2
while 1 do while r!=1 do count[r-1] = r r -= 1 end while if not (perm1[1]=1 or perm1[n]=n) then perm = perm1 flipsCount = 0 k = perm[1] while k!=1 do k2 = floor((k+1)/2) perm = reverse(perm[1..k]) & perm[k+1..n] flipsCount += 1 k = perm[1] end while if flipsCount>maxFlipsCount then maxFlipsCount = flipsCount end if end if -- Use incremental change to generate another permutation while 1 do if r>n then return maxFlipsCount end if perm0 = perm1[1] j2 = 1 while j2<r do j = j2+1 perm1[j2] = perm1[j] j2 = j end while perm1[r] = perm0 count[r] = count[r]-1 if count[r]>1 then exit else r += 1 end if end while end while
end function -- fannkuch
for i=1 to 10 do
? fannkuch(i)
end for</lang>
- Output:
0 1 2 4 7 10 16 22 30 38
PicoLisp
<lang PicoLisp>(de fannkuch (N)
(let (Lst (range 1 N) L Lst Max) (recur (L) # Permute (if (cdr L) (do (length L) (recurse (cdr L)) (rot L) ) (zero N) # For each permutation (for (P (copy Lst) (> (car P) 1) (flip P (car P))) (inc 'N) ) (setq Max (max N Max)) ) ) Max ) )
(for I 10
(println I (fannkuch I)) )</lang>
Output:
1 0 2 1 3 2 4 4 5 7 6 10 7 16 8 22 9 30 10 38
PL/I
<lang PL/I> (subscriptrange): topswap: procedure options (main); /* 12 November 2013 */
declare cards(*) fixed (2) controlled, t fixed (2); declare dealt(*) bit(1) controlled; declare (count, i, m, n, c1, c2) fixed binary; declare random builtin;
do n = 1 to 10; allocate cards(n), dealt(n); /* Take the n cards, in order ... */ do i = 1 to n; cards(i) = i; end; /* ... and shuffle them. */ do i = 1 to n; c1 = random*n+1; c2 = random*n+1; t = cards(c1); cards(c1) = cards(c2); cards(c2) = t; end; /* If '1' is the first card, game is trivial; swap it with another. */ if cards(1) = 1 & n > 1 then do; t = cards(1); cards(1) = cards(2); cards(2) = t; end;
count = 0; do until (cards(1) = 1); /* take the value of the first card, M, and reverse the first M cards. */ m = cards(1); do i = 1 to m/2; t = cards(i); cards(i) = cards(m-i+1); cards(m-i+1) = t; end; count = count + 1; end; put skip edit (n, ':', count) (f(2), a, f(4)); end;
end topswap; </lang>
1: 1 2: 1 3: 2 4: 2 5: 4 6: 2 7: 1 8: 9 9: 16 10: 1
Potion
<lang potion>range = (a, b):
i = 0, l = list(b-a+1) while (a + i <= b): l (i) = a + i++. l.
fannkuch = (n):
flips = 0, maxf = 0, k = 0, m = n - 1, r = n perml = range(0, n), count = list(n), perm = list(n)
loop: while (r != 1): count (r-1) = r r--.
if (perml (0) != 0 and perml (m) != m): flips = 0, i = 1 while (i < n): perm (i) = perml (i) i++. k = perml (0) loop: i = 1, j = k - 1 while (i < j): t = perm (i), perm (i) = perm (j), perm (j) = t i++, j--. flips++ j = perm (k), perm (k) = k, k = j if (k == 0): break. . if (flips > maxf): maxf = flips. .
loop: if (r == n): (n, maxf) say return (maxf).
i = 0, j = perml (0) while (i < r): k = i + 1 perml (i) = perml (k) i = k. perml (r) = j
j = count (r) - 1 count (r) = j if (j > 0): break. r++
_ n
n = argv(1) number if (n<1): n=10. fannkuch(n) </lang>
Output follows that of Perl6 and Python, ~2.5x faster than perl5
Python
This solution uses cards numbered from 0..n-1 and variable p0 is introduced as a speed optimisation <lang python>>>> from itertools import permutations >>> def f1(p): i = 0 while True: p0 = p[0] if p0 == 1: break p[:p0] = p[:p0][::-1] i += 1 return i
>>> def fannkuch(n): return max(f1(list(p)) for p in permutations(range(1, n+1)))
>>> for n in range(1, 11): print(n,fannkuch(n))
1 0 2 1 3 2 4 4 5 7 6 10 7 16 8 22 9 30 10 38 >>> </lang>
Python: Faster Version
<lang python>try:
import psyco psyco.full()
except ImportError:
pass
best = [0] * 16
def try_swaps(deck, f, s, d, n):
if d > best[n]: best[n] = d
i = 0 k = 1 << s while s: k >>= 1 s -= 1 if deck[s] == -1 or deck[s] == s: break i |= k if (i & f) == i and d + best[s] <= best[n]: return d s += 1
deck2 = list(deck) k = 1 for i2 in xrange(1, s): k <<= 1 if deck2[i2] == -1: if f & k: continue elif deck2[i2] != i2: continue
deck[i2] = i2 deck2[:i2 + 1] = reversed(deck[:i2 + 1]) try_swaps(deck2, f | k, s, 1 + d, n)
def topswops(n):
best[n] = 0 deck0 = [-1] * 16 deck0[0] = 0 try_swaps(deck0, 1, n, 0, n) return best[n]
for i in xrange(1, 13):
print "%2d: %d" % (i, topswops(i))</lang>
- Output:
1: 0 2: 1 3: 2 4: 4 5: 7 6: 10 7: 16 8: 22 9: 30 10: 38 11: 51 12: 65
Racket
Simple search, only "optimization" is to consider only all-misplaced permutations (as in the alternative Haskell solution), which shaves off around 2 seconds (from ~5).
<lang Racket>
- lang racket
(define (all-misplaced? l)
(for/and ([x (in-list l)] [n (in-naturals 1)]) (not (= x n))))
(define (topswops n)
(for/fold ([m 0]) ([p (in-permutations (range 1 (add1 n)))] #:when (all-misplaced? p)) (let loop ([p p] [n 0]) (if (= 1 (car p)) (max n m) (loop (let loop ([l '()] [r p] [n (car p)]) (if (zero? n) (append l r) (loop (cons (car r) l) (cdr r) (sub1 n)))) (add1 n))))))
(for ([i (in-range 1 11)]) (printf "~a\t~a\n" i (topswops i))) </lang>
Output:
1 0 2 1 3 2 4 4 5 7 6 10 7 16 8 22 9 30 10 38
REXX
The decks function is a modified permSets (permutation sets) subroutine,
and is optimized somewhat to take advantage by eliminating one-swop "decks".
<lang rexx>/*REXX program generates N decks of numbered cards and finds the maximum "swops". */
parse arg things .; if things== then things=10
do n=1 for things; #=decks(n, n) /*create a (things) number of "decks". */ mx= n\==1 /*handle the case of a one-card deck.*/ do i=1 for #; p=swops(!.i) /*compute the SWOPS for this iteration.*/ if p>mx then mx=p /*This a new maximum? Use a new max. */ end /*i*/ say '──────── maximum swops for a deck of' right(n,2) ' cards is' right(mx,4) end /*n*/
exit /*stick a fork in it, we're all done. */ /*──────────────────────────────────────────────────────────────────────────────────────*/ decks: procedure expose !.; parse arg x,y,,$ @. /* X things taken Y at a time. */
#=0; call .decks 1 /* [↑] initialize $ & @. to null.*/ return # /*return number of permutations (decks)*/
.decks: procedure expose !. @. x y $ #; parse arg ?
if ?>y then do; _=@.1; do j=2 for y-1; _=_ @.j; end /*j*/; #=#+1; !.#=_ end else do; qm=?-1 if ?==1 then qs=2 /*don't use 1-swops that start with 1 */ else if @.1==? then qs=2 /*skip the 1-swops: 3 x 1 x ···*/ else qs=1 do q=qs to x /*build the permutations recursively. */ do k=1 for qm; if @.k==q then iterate q end /*k*/ @.?=q; call .decks ? + 1 end /*q*/ end return
/*──────────────────────────────────────────────────────────────────────────────────────*/ swops: parse arg z; do u=1; parse var z t .; if length(t)==2 then t=x2d(t)
if word(z, t)==1 then return u /*found unity at T. */ do h=10 to things; if pos(h, z)==0 then iterate z=changestr(h, z, d2x(h) ) /* [↑] any H's in Z ? */ end /*h*/ z=reverse(subword(z, 1, t)) subword(z, t+1) end /*u*/</lang>
Some older REXXes don't have a changestr bif, so one is included here ───► CHANGESTR.REX.
- output when using the default input:
──────── maximum swops for a deck of 1 cards is 0 ──────── maximum swops for a deck of 2 cards is 1 ──────── maximum swops for a deck of 3 cards is 2 ──────── maximum swops for a deck of 4 cards is 4 ──────── maximum swops for a deck of 5 cards is 7 ──────── maximum swops for a deck of 6 cards is 10 ──────── maximum swops for a deck of 7 cards is 16 ──────── maximum swops for a deck of 8 cards is 22 ──────── maximum swops for a deck of 9 cards is 30 ──────── maximum swops for a deck of 10 cards is 38
Ruby
<lang ruby>def f1(a)
i = 0 while (a0 = a[0]) > 1 a[0...a0] = a[0...a0].reverse i += 1 end i
end
def fannkuch(n)
[*1..n].permutation.map{|a| f1(a)}.max
end
for n in 1..10
puts "%2d : %d" % [n, fannkuch(n)]
end</lang>
- Output:
1 : 0 2 : 1 3 : 2 4 : 4 5 : 7 6 : 10 7 : 16 8 : 22 9 : 30 10 : 38
Faster Version
<lang ruby>def try_swaps(deck, f, d, n)
@best[n] = d if d > @best[n] (n-1).downto(0) do |i| break if deck[i] == -1 || deck[i] == i return if d + @best[i] <= @best[n] end deck2 = deck.dup for i in 1...n k = 1 << i if deck2[i] == -1 next if f & k != 0 elsif deck2[i] != i next end deck2[0] = i deck2[1..i] = deck[0...i].reverse try_swaps(deck2, f | k, d+1, n) end
end
def topswops(n)
@best[n] = 0 deck0 = [-1] * (n + 1) try_swaps(deck0, 1, 0, n) @best[n]
end
@best = [0] * 16 for i in 1..10
puts "%2d : %d" % [i, topswops(i)]
end</lang>
Scala
<lang Scala>object Fannkuch extends App {
def fannkuchen(l: List[Int], n: Int, i: Int, acc: Int): Int = { def flips(l: List[Int]): Int = (l: @unchecked) match { case 1 :: ls => 0 case (n :: ls) => val splitted = l.splitAt(n) flips(splitted._2.reverse_:::(splitted._1)) + 1 }
def rotateLeft(l: List[Int]) = l match { case Nil => List() case x :: xs => xs ::: List(x) }
if (i >= n) acc else { if (n == 1) acc.max(flips(l)) else { val split = l.splitAt(n) fannkuchen(rotateLeft(split._1) ::: split._2, n, i + 1, fannkuchen(l, n - 1, 0, acc)) } } } // def fannkuchen(
val result = (1 to 10).map(i => (i, fannkuchen(List.range(1, i + 1), i, 0, 0))) println("Computing results...") result.foreach(x => println(s"Pfannkuchen(${x._1})\t= ${x._2}")) assert(result == Vector((1, 0), (2, 1), (3, 2), (4, 4), (5, 7), (6, 10), (7, 16), (8, 22), (9, 30), (10, 38)), "Bad results") println(s"Successfully completed without errors. [total ${scala.compat.Platform.currentTime - executionStart} ms]")
}</lang>
- Output:
Computing results... Pfannkuchen(1) = 0 Pfannkuchen(2) = 1 Pfannkuchen(3) = 2 Pfannkuchen(4) = 4 Pfannkuchen(5) = 7 Pfannkuchen(6) = 10 Pfannkuchen(7) = 16 Pfannkuchen(8) = 22 Pfannkuchen(9) = 30 Pfannkuchen(10) = 38 Successfully completed without errors. [total 7401 ms] Process finished with exit code 0
Tcl
Probably an integer overflow at n=10.
<lang tcl>package require struct::list
proc swap {listVar} {
upvar 1 $listVar list set n [lindex $list 0] for {set i 0; set j [expr {$n-1}]} {$i<$j} {incr i;incr j -1} {
set tmp [lindex $list $i] lset list $i [lindex $list $j] lset list $j $tmp
}
}
proc swaps {list} {
for {set i 0} {[lindex $list 0] > 1} {incr i} {
swap list
} return $i
}
proc topswops list {
set n 0 ::struct::list foreachperm p $list {
set n [expr {max($n,[swaps $p])}]
} return $n
}
proc topswopsTo n {
puts "n\ttopswops(n)" for {set i 1} {$i <= $n} {incr i} {
puts $i\t[topswops [lappend list $i]]
}
}
topswopsTo 10</lang>
- Output:
n topswops(n) 1 0 2 1 3 2 4 4 5 7 6 10 7 16 8 22 9 30 10 38
XPL0
<lang XPL0>code ChOut=8, CrLf=9, IntOut=11; int N, Max, Card1(16), Card2(16);
proc Topswop(D); \Conway's card swopping game int D; \depth of recursion int I, J, C, T; [if D # N then \generate N! permutations of 1..N in Card1
[for I:= 0 to N-1 do [for J:= 0 to D-1 do \check if object (letter) already used if Card1(J) = I+1 then J:=100; if J < 100 then [Card1(D):= I+1; \card number not used so append it Topswop(D+1); \recurse next level deeper ]; ]; ]
else [\determine number of topswops to get card 1 at beginning
for I:= 0 to N-1 do Card2(I):= Card1(I); \make working copy of deck C:= 0; \initialize swop counter while Card2(0) # 1 do [I:= 0; J:= Card2(0)-1; while I < J do [T:= Card2(I); Card2(I):= Card2(J); Card2(J):= T; I:= I+1; J:= J-1; ]; C:= C+1; ]; if C>Max then Max:= C; ];
];
[for N:= 1 to 10 do
[Max:= 0; Topswop(0); IntOut(0, N); ChOut(0, ^ ); IntOut(0, Max); CrLf(0); ];
]</lang>
- Output:
1 0 2 1 3 2 4 4 5 7 6 10 7 16 8 22 9 30 10 38
XPL0: Faster Version
<lang XPL0>code CrLf=9, IntOut=11, Text=12; int N, D, Best(16);
proc TrySwaps(A, F, S); int A, F, S; int B(16), I, J, K; [if D > Best(N) then Best(N):= D; loop [if A(S)=-1 ! A(S)=S then quit;
if D+Best(S) <= Best(N) then return; if S = 0 then quit; S:= S-1; ];
D:= D+1; for I:= 0 to S do B(I):= A(I); K:= 1; for I:= 1 to S do
[K:= K<<1; if B(I)=-1 & (F&K)=0 ! B(I)=I then [J:= I; B(0):= J; while J do [J:= J-1; B(I-J):= A(J)]; TrySwaps(B, F!K, S); ]; ];
D:= D-1; ];
int I, X(16); [for I:= 0 to 16-1 do
[X(I):= -1; Best(I):= 0];
X(0):= 0; for N:= 1 to 13 do
[D:= 0; TrySwaps(X, 1, N-1); IntOut(0, N); Text(0, ": "); IntOut(0, Best(N)); CrLf(0); ];
]</lang>
- Output:
1: 0 2: 1 3: 2 4: 4 5: 7 6: 10 7: 16 8: 22 9: 30 10: 38 11: 51 12: 65 13: 80
zkl
Slow version <lang zkl>fcn topswops(n){
flip:=fcn(xa){ if (not xa[0]) return(0); xa.reverse(0,xa[0]+1); // inplace, ~4x faster than making new lists return(1 + self.fcn(xa)); }; (0).pump(n,List):Utils.Helpers.permute(_).pump(List,"copy",flip).reduce("max");
}
foreach n in ([1 .. 10]){ println(n, ": ", topswops(n)) }</lang>
- Output:
1: 0 2: 1 3: 2 4: 4 5: 7 6: 10 7: 16 8: 22 9: 30 10: 38