Order by pair comparisons
You are encouraged to solve this task according to the task description, using any language you may know.
Sorting Algorithm
This is a sorting algorithm. It may be applied to a set of data in order to sort it.
For comparing various sorts, see compare sorts.
For other sorting algorithms, see sorting algorithms, or:
Heap sort | Merge sort | Patience sort | Quick sort
O(n log2n) sorts
Shell Sort
O(n2) sorts
Bubble sort |
Cocktail sort |
Cocktail sort with shifting bounds |
Comb sort |
Cycle sort |
Gnome sort |
Insertion sort |
Selection sort |
Strand sort
other sorts
Bead sort |
Bogo sort |
Common sorted list |
Composite structures sort |
Custom comparator sort |
Counting sort |
Disjoint sublist sort |
External sort |
Jort sort |
Lexicographical sort |
Natural sorting |
Order by pair comparisons |
Order disjoint list items |
Order two numerical lists |
Object identifier (OID) sort |
Pancake sort |
Quickselect |
Permutation sort |
Radix sort |
Ranking methods |
Remove duplicate elements |
Sleep sort |
Stooge sort |
[Sort letters of a string] |
Three variable sort |
Topological sort |
Tree sort
Assume we have a set of items that can be sorted into an order by the user.
The user is presented with pairs of items from the set in no order, the user states which item is less than, equal to, or greater than the other (with respect to their relative positions if fully ordered).
Write a function that given items that the user can order, asks the user to give the result of comparing two items at a time and uses the comparison results to eventually return the items in order.
Try and minimise the comparisons the user is asked for.
Show on this page, the function ordering the colours of the rainbow:
violet red green indigo blue yellow orange
The correct ordering being:
red orange yellow green blue indigo violet
Note:
- Asking for/receiving user comparisons is a part of the task.
- Code inputs should not assume an ordering.
- The seven colours can form twenty-one different pairs.
- A routine that does not ask the user "too many" comparison questions should be used.
C
Using qsort; not very efficient <lang c>#include <stdio.h>
- include <string.h>
- include <stdlib.h>
int interactiveCompare(const void *x1, const void *x2) {
const char *s1 = *(const char * const *)x1; const char *s2 = *(const char * const *)x2; static int count = 0; printf("(%d) Is %s <, ==, or > %s? Answer -1, 0, or 1: ", ++count, s1, s2); int response; scanf("%d", &response); return response;
}
void printOrder(const char *items[], int len) {
printf("{ "); for (int i = 0; i < len; ++i) printf("%s ", items[i]); printf("}\n");
}
int main(void) {
const char *items[] = { "violet", "red", "green", "indigo", "blue", "yellow", "orange" };
qsort(items, sizeof(items)/sizeof(*items), sizeof(*items), interactiveCompare); printOrder(items, sizeof(items)/sizeof(*items)); return 0;
}</lang>
- Output:
(1) Is violet <, ==, or > red? Answer -1, 0, or 1: 1 (2) Is violet <, ==, or > green? Answer -1, 0, or 1: 1 (3) Is red <, ==, or > green? Answer -1, 0, or 1: -1 (4) Is violet <, ==, or > indigo? Answer -1, 0, or 1: 1 (5) Is green <, ==, or > indigo? Answer -1, 0, or 1: -1 (6) Is violet <, ==, or > blue? Answer -1, 0, or 1: 1 (7) Is indigo <, ==, or > blue? Answer -1, 0, or 1: 1 (8) Is green <, ==, or > blue? Answer -1, 0, or 1: -1 (9) Is violet <, ==, or > yellow? Answer -1, 0, or 1: 1 (10) Is indigo <, ==, or > yellow? Answer -1, 0, or 1: 1 (11) Is blue <, ==, or > yellow? Answer -1, 0, or 1: 1 (12) Is green <, ==, or > yellow? Answer -1, 0, or 1: 1 (13) Is red <, ==, or > yellow? Answer -1, 0, or 1: -1 (14) Is violet <, ==, or > orange? Answer -1, 0, or 1: 1 (15) Is indigo <, ==, or > orange? Answer -1, 0, or 1: 1 (16) Is blue <, ==, or > orange? Answer -1, 0, or 1: 1 (17) Is green <, ==, or > orange? Answer -1, 0, or 1: 1 (18) Is yellow <, ==, or > orange? Answer -1, 0, or 1: 1 (19) Is red <, ==, or > orange? Answer -1, 0, or 1: -1 { red orange yellow green blue indigo violet }
C++
C++: Binary search insertion sort
<lang cpp>#include <algorithm>
- include <iostream>
- include <vector>
using namespace std;
bool InteractiveCompare(const string& s1, const string& s2) {
if(s1 == s2) return false; // don't ask to compare items that are the same static int count = 0; string response; cout << "(" << ++count << ") Is " << s1 << " < " << s2 << "? "; getline(cin, response); return !response.empty() && response.front() == 'y';
}
void PrintOrder(const vector<string>& items) {
cout << "{ "; for(auto& item : items) cout << item << " "; cout << "}\n";
}
int main() {
const vector<string> items { "violet", "red", "green", "indigo", "blue", "yellow", "orange" }; vector<string> sortedItems; // Use a binary insertion sort to order the items. It should ask for // close to the minimum number of questions required for(auto& item : items) { cout << "Inserting '" << item << "' into "; PrintOrder(sortedItems); // lower_bound performs the binary search using InteractiveCompare to // rank the items auto spotToInsert = lower_bound(sortedItems.begin(), sortedItems.end(), item, InteractiveCompare); sortedItems.insert(spotToInsert, item); } PrintOrder(sortedItems); return 0;
}</lang>
- Output:
Inserting 'violet' into { } Inserting 'red' into { violet } (1) Is violet < red? n Inserting 'green' into { red violet } (2) Is violet < green? n (3) Is red < green? y Inserting 'indigo' into { red green violet } (4) Is green < indigo? y (5) Is violet < indigo? n Inserting 'blue' into { red green indigo violet } (6) Is indigo < blue? n (7) Is green < blue? y Inserting 'yellow' into { red green blue indigo violet } (8) Is blue < yellow? n (9) Is green < yellow? n (10) Is red < yellow? y Inserting 'orange' into { red yellow green blue indigo violet } (11) Is blue < orange? n (12) Is yellow < orange? n (13) Is red < orange? y { red orange yellow green blue indigo violet }
C++: STL sort with custom comparator
<lang cpp>#include <algorithm>
- include <iostream>
- include <vector>
using namespace std;
bool InteractiveCompare(const string& s1, const string& s2) {
if(s1 == s2) return false; // don't ask to compare items that are the same static int count = 0; string response; cout << "(" << ++count << ") Is " << s1 << " < " << s2 << "? "; getline(cin, response); return !response.empty() && response.front() == 'y';
}
void PrintOrder(const vector<string>& items) {
cout << "{ "; for(auto& item : items) cout << item << " "; cout << "}\n";
}
int main() {
vector<string> items { "violet", "red", "green", "indigo", "blue", "yellow", "orange" }; sort(items.begin(), items.end(), InteractiveCompare); PrintOrder(items); return 0;
}</lang>
- Output:
(1) Is indigo < violet? y (2) Is orange < indigo? y (3) Is orange < indigo? y (4) Is red < indigo? y (5) Is green < indigo? y (6) Is yellow < indigo? y (7) Is blue < indigo? y (8) Is blue < indigo? y (9) Is red < orange? y (10) Is green < red? n (11) Is green < orange? n (12) Is yellow < green? y (13) Is yellow < orange? n (14) Is blue < green? n { red orange yellow green blue indigo violet }
Commodore BASIC
<lang basic>100 REM SORT BY COMPARISON 110 DIM IN$(6), OU$(6) 120 FOR I=0 TO 6:READ IN$(I): NEXT I 130 DATA VIOLET,RED,GREEN,INDIGO,BLUE,YELLOW,ORANGE 140 OU$(0)=IN$(0):N=1 150 FOR I=1 TO 6 160 : IN$=IN$(I) 180 : GOSUB 390 190 : FOR J=0 TO N-1 200 : OU$ = OU$(J) 210 : GOSUB 340 220 : IF R>=0 THEN 280 230 : FOR K=N TO J+1 STEP -1 240 : OU$(K) = OU$(K-1) 250 : NEXT K 260 : OU$(J) = IN$ 270 : GOTO 300 280 : NEXT J 290 : OU$(N) = IN$ 300 : N=N+1 310 NEXT I 320 GOSUB 390 330 END 340 PRINT "IS "IN$" < "OU$"? (Y/N)"; 350 GET K$: IF K$<>"Y" AND K$<>"N" THEN 350 360 PRINT K$ 370 R = K$="Y" 380 RETURN 390 PRINT "("; 400 IF N=1 THEN 420 410 FOR Q=0 TO N-2:PRINT OU$(Q)",";:NEXT Q 420 PRINT OU$(N-1)")" 430 RETURN</lang>
- Output:
IS RED < VIOLET? (Y/N)Y IS GREEN < RED? (Y/N)N IS GREEN < VIOLET? (Y/N)Y IS INDIGO < RED? (Y/N)N IS INDIGO < GREEN? (Y/N)N IS INDIGO < VIOLET? (Y/N)Y IS BLUE < RED? (Y/N)N IS BLUE < GREEN? (Y/N)N IS BLUE < INDIGO? (Y/N)Y IS YELLOW < RED? (Y/N)N IS YELLOW < GREEN? (Y/N)Y IS ORANGE < RED? (Y/N)N IS ORANGE < YELLOW? (Y/N)Y (RED,ORANGE,YELLOW,GREEN,BLUE,INDIGO,VIOLET)
F#
<lang fsharp> // Order by pair comparisons. Nigel Galloway: April 23rd., 2021 type colours= Violet |Red |Green |Indigo |Blue |Yellow |Orange let fN,fG=let mutable z=0 in ((fun()->z),(fun n g->z<-z+1; compare n g)) printfn "[Red;Orange;Yellow;Green;Blue;Indigo;Violet] sorted to %A using %d comparisons" ([Red;Orange;Yellow;Green;Blue;Indigo;Violet]|>List.sortWith(fun n g->fG n g)) (fN()) </lang>
- Output:
[Red;Orange;Yellow;Green;Blue;Indigo;Violet] sorted to [Violet; Red; Green; Indigo; Blue; Yellow; Orange] using 25 comparisons
Factor
Asking the user for an ordering specifier inside a custom comparator:
<lang factor>USING: formatting io kernel math.order prettyprint qw sorting ;
qw{ violet red green indigo blue yellow orange } [ "Is %s > %s? (y/n) " printf readln "y" = +gt+ +lt+ ? ] sort .</lang>
- Output:
Is violet > red? (y/n) y Is green > indigo? (y/n) n Is blue > yellow? (y/n) y Is red > green? (y/n) n Is violet > green? (y/n) y Is violet > indigo? (y/n) y Is yellow > orange? (y/n) y Is red > orange? (y/n) n Is green > orange? (y/n) y Is green > yellow? (y/n) y Is green > blue? (y/n) n Is indigo > blue? (y/n) y { "red" "orange" "yellow" "green" "blue" "indigo" "violet" }
Go
Go: Binary search insertion sort
<lang go>package main
import (
"fmt" "sort" "strings"
)
var count int = 0
func interactiveCompare(s1, s2 string) bool {
count++ fmt.Printf("(%d) Is %s < %s? ", count, s1, s2) var response string _, err := fmt.Scanln(&response) return err == nil && strings.HasPrefix(response, "y")
}
func main() {
items := []string{"violet", "red", "green", "indigo", "blue", "yellow", "orange"} var sortedItems []string // Use a binary insertion sort to order the items. It should ask for // close to the minimum number of questions required for _, item := range items { fmt.Printf("Inserting '%s' into %s\n", item, sortedItems) // sort.Search performs the binary search using interactiveCompare to // rank the items spotToInsert := sort.Search(len(sortedItems), func(i int) bool { return interactiveCompare(item, sortedItems[i]) }) sortedItems = append(sortedItems[:spotToInsert], append([]string{item}, sortedItems[spotToInsert:]...)...) } fmt.Println(sortedItems)
}</lang>
- Output:
Inserting 'violet' into [] Inserting 'red' into [violet] (1) Is red < violet? y Inserting 'green' into [red violet] (2) Is green < violet? y (3) Is green < red? n Inserting 'indigo' into [red green violet] (4) Is indigo < green? n (5) Is indigo < violet? y Inserting 'blue' into [red green indigo violet] (6) Is blue < indigo? y (7) Is blue < green? n Inserting 'yellow' into [red green blue indigo violet] (8) Is yellow < blue? y (9) Is yellow < green? y (10) Is yellow < red? n Inserting 'orange' into [red yellow green blue indigo violet] (11) Is orange < blue? y (12) Is orange < yellow? y (13) Is orange < red? n [red orange yellow green blue indigo violet]
Go: Standard sort with custom comparator
<lang go>package main
import (
"fmt" "sort" "strings"
)
var count int = 0
type sortable []string func (s sortable) Len() int { return len(s) } func (s sortable) Swap(i, j int) { s[i], s[j] = s[j], s[i] } func (s sortable) Less(i, j int) bool {
s1, s2 := s[i], s[j] count++ fmt.Printf("(%d) Is %s < %s? ", count, s1, s2) var response string _, err := fmt.Scanln(&response) return err == nil && strings.HasPrefix(response, "y")
}
func main() {
items := sortable{"violet", "red", "green", "indigo", "blue", "yellow", "orange"} sort.Sort(items) fmt.Println(items)
}</lang>
- Output:
(1) Is orange < violet? y (2) Is red < orange? y (3) Is green < orange? n (4) Is indigo < green? n (5) Is blue < indigo? y (6) Is blue < green? n (7) Is yellow < indigo? y (8) Is yellow < blue? y (9) Is yellow < green? y (10) Is yellow < orange? n (11) Is violet < indigo? n [red orange yellow green blue indigo violet]
Java
Java: Binary search insertion sort
<lang java>import java.util.*;
public class SortComp1 {
public static void main(String[] args) { List<String> items = Arrays.asList("violet", "red", "green", "indigo", "blue", "yellow", "orange"); List<String> sortedItems = new ArrayList<>(); Comparator<String> interactiveCompare = new Comparator<String>() { int count = 0; Scanner s = new Scanner(System.in); public int compare(String s1, String s2) { System.out.printf("(%d) Is %s <, =, or > %s. Answer -1, 0, or 1: ", ++count, s1, s2); return s.nextInt(); } }; for (String item : items) { System.out.printf("Inserting '%s' into %s\n", item, sortedItems); int spotToInsert = Collections.binarySearch(sortedItems, item, interactiveCompare); // when item does not equal an element in sortedItems, // it returns bitwise complement of insertion point if (spotToInsert < 0) spotToInsert = ~spotToInsert; sortedItems.add(spotToInsert, item); } System.out.println(sortedItems); }
}</lang>
- Output:
Inserting 'violet' into [] Inserting 'red' into [violet] (1) Is violet <, =, or > red. Answer -1, 0, or 1: 1 Inserting 'green' into [red, violet] (2) Is red <, =, or > green. Answer -1, 0, or 1: -1 (3) Is violet <, =, or > green. Answer -1, 0, or 1: 1 Inserting 'indigo' into [red, green, violet] (4) Is green <, =, or > indigo. Answer -1, 0, or 1: -1 (5) Is violet <, =, or > indigo. Answer -1, 0, or 1: 1 Inserting 'blue' into [red, green, indigo, violet] (6) Is green <, =, or > blue. Answer -1, 0, or 1: -1 (7) Is indigo <, =, or > blue. Answer -1, 0, or 1: 1 Inserting 'yellow' into [red, green, blue, indigo, violet] (8) Is blue <, =, or > yellow. Answer -1, 0, or 1: 1 (9) Is red <, =, or > yellow. Answer -1, 0, or 1: -1 (10) Is green <, =, or > yellow. Answer -1, 0, or 1: 1 Inserting 'orange' into [red, yellow, green, blue, indigo, violet] (11) Is green <, =, or > orange. Answer -1, 0, or 1: 1 (12) Is red <, =, or > orange. Answer -1, 0, or 1: -1 (13) Is yellow <, =, or > orange. Answer -1, 0, or 1: 1 [red, orange, yellow, green, blue, indigo, violet]
Java: Standard sort with custom comparator
<lang java>import java.util.*;
public class OrderByPair {
public static void main(String[] args) { List<String> items = Arrays.asList("violet", "red", "green", "indigo", "blue", "yellow", "orange"); Collections.sort(items, new Comparator<String>() { int count = 0; Scanner s = new Scanner(System.in); public int compare(String s1, String s2) { System.out.printf("(%d) Is %s <, =, or > %s. Answer -1, 0, or 1: ", ++count, s1, s2); return s.nextInt(); } }); System.out.println(items); }
}</lang>
- Output:
(1) Is red <, =, or > violet. Answer -1, 0, or 1: -1 (2) Is green <, =, or > red. Answer -1, 0, or 1: 1 (3) Is green <, =, or > violet. Answer -1, 0, or 1: -1 (4) Is green <, =, or > red. Answer -1, 0, or 1: 1 (5) Is indigo <, =, or > green. Answer -1, 0, or 1: 1 (6) Is indigo <, =, or > violet. Answer -1, 0, or 1: -1 (7) Is blue <, =, or > indigo. Answer -1, 0, or 1: -1 (8) Is blue <, =, or > green. Answer -1, 0, or 1: 1 (9) Is yellow <, =, or > blue. Answer -1, 0, or 1: -1 (10) Is yellow <, =, or > green. Answer -1, 0, or 1: -1 (11) Is yellow <, =, or > red. Answer -1, 0, or 1: 1 (12) Is orange <, =, or > blue. Answer -1, 0, or 1: -1 (13) Is orange <, =, or > yellow. Answer -1, 0, or 1: 1 (14) Is orange <, =, or > green. Answer -1, 0, or 1: 1 [red, yellow, green, orange, blue, indigo, violet]
Julia
<lang julia>const nrequests = [0] const ordering = Dict("violet" => 7, "red" => 1, "green" => 4, "indigo" => 6, "blue" => 5,
"yellow" => 3, "orange" => 2)
function tellmeifgt(x, y)
nrequests[1] += 1 while true print("Is $x greater than $y? (Y/N) => ") s = strip(readline()) if length(s) > 0 (s[1] == 'Y' || s[1] == 'y') && return true (s[1] == 'N' || s[1] == 'n') && return false end end
end
function orderbypair!(a::Vector)
incr = div(length(a), 2) while incr > 0 for i in incr+1:length(a) j = i tmp = a[i] while j > incr && tellmeifgt(a[j - incr], tmp) a[j] = a[j-incr] j -= incr end a[j] = tmp end if incr == 2 incr = 1 else incr = floor(Int, incr * 5.0 / 11) end end return a
end
const words = String.(split("violet red green indigo blue yellow orange", r"\s+")) println("Unsorted: $words") println("Sorted: $(orderbypair!(words)). Total requests: $(nrequests[1]).")
</lang>
- Output:
Is violet greater than indigo? (Y/N) => y Is red greater than blue? (Y/N) => n Is green greater than yellow? (Y/N) => y Is violet greater than orange? (Y/N) => y Is indigo greater than orange? (Y/N) => y Is orange greater than red? (Y/N) => y Is orange greater than yellow? (Y/N) => n Is yellow greater than indigo? (Y/N) => n Is indigo greater than blue? (Y/N) => y Is yellow greater than blue? (Y/N) => n Is indigo greater than green? (Y/N) => y Is blue greater than green? (Y/N) => y Is yellow greater than green? (Y/N) => n Is indigo greater than violet? (Y/N) => n Sorted: ["red", "orange", "yellow", "green", "blue", "indigo", "violet"]. Total requests: 14.
Nim
Using a list filled by binary insertion and a custom comparison function. <lang Nim>import algorithm, strformat, strutils
let list = ["violet", "red", "green", "indigo", "blue", "yellow", "orange"]
var count = 0
proc comp(x, y: string): int =
if x == y: return 0 inc count while true: stdout.write &"{count:>2}) Is {x} less than {y} (y/n)? " let answer = stdin.readLine()[0] case answer of 'y': return -1 of 'n': return 1 else: echo "Incorrect answer."
var sortedList: seq[string]
for elem in list:
sortedList.insert(elem, sortedList.upperBound(elem, comp))
echo "Sorted list: ", sortedList.join(", ")</lang>
- Output:
1) Is violet less than red (y/n)? n 2) Is violet less than green (y/n)? n 3) Is red less than green (y/n)? n 4) Is red less than indigo (y/n)? n 5) Is green less than indigo (y/n)? y 6) Is red less than blue (y/n)? n 7) Is indigo less than blue (y/n)? n 8) Is green less than blue (y/n)? n 9) Is indigo less than yellow (y/n)? y 10) Is violet less than yellow (y/n)? y 11) Is red less than orange (y/n)? n 12) Is green less than orange (y/n)? y 13) Is indigo less than orange (y/n)? y Sorted list: blue, green, indigo, orange, red, violet, yellow
Perl
<lang perl>#!/usr/bin/perl
use strict; # https://rosettacode.org/wiki/Order_by_pair_comparisons use warnings;
sub ask
{ while( 1 ) { print "Compare $a to $b [<,=,>]: "; <STDIN> =~ /[<=>]/ and return +{qw( < -1 = 0 > 1 )}->{$&}; } }
my @sorted = sort ask qw( violet red green indigo blue yellow orange ); print "sorted: @sorted\n";</lang>
- Output:
Compare violet to red [<,=,>]: > Compare green to indigo [<,=,>]: < Compare blue to yellow [<,=,>]: > Compare red to green [<,=,>]: < Compare green to violet [<,=,>]: < Compare violet to indigo [<,=,>]: ? Compare violet to indigo [<,=,>]: > Compare yellow to orange [<,=,>]: > Compare red to orange [<,=,>]: < Compare orange to green [<,=,>]: < Compare green to yellow [<,=,>]: > Compare green to blue [<,=,>]: < Compare indigo to blue [<,=,>]: > sorted: red orange yellow green blue indigo violet
Phix
The number of questions asked is entirely dependent on how the initial order marries in with the sorting algorithm.
This needs just 6 questions to handle an already in-order or only first two items swapped list.
I picked an initial ordering that requires a fairly easy to remember set of answers: 4Y then alternate.
The builtin sort(s) use an initial gap of 10%, ultimately balancing #comparisons against cache hits, which leads to a wider range of #questions, as said best case 6, worst case 21. A better match to the narrower range of Python (I think 10..14) could probably be made using a copy of custom_sort (it is only 52 lines) with an initial 50% gap.
integer qn = 0 function ask(string a, b) qn += 1 printf(1,"%d: Is %s < %s (Y/N)?:",{qn,a,b}) integer ch = upper(wait_key()) printf(1,"%s\n",ch) return iff(ch='Y'?-1:1) end function ?custom_sort(ask,split("violet orange red yellow green blue indigo"))
- Output:
1: Is orange < violet (Y/N)?:Y 2: Is red < violet (Y/N)?:Y 3: Is red < orange (Y/N)?:Y 4: Is yellow < violet (Y/N)?:Y 5: Is yellow < orange (Y/N)?:N 6: Is green < violet (Y/N)?:Y 7: Is green < yellow (Y/N)?:N 8: Is blue < violet (Y/N)?:Y 9: Is blue < green (Y/N)?:N 10: Is indigo < violet (Y/N)?:Y 11: Is indigo < blue (Y/N)?:N {"red","orange","yellow","green","blue","indigo","violet"}
Python
Python: Binary insertion
Uses binary search to insert successive items into a growing ordered list. Comparisons are asked for.
<lang python>def _insort_right(a, x, q):
""" Insert item x in list a, and keep it sorted assuming a is sorted. If x is already in a, insert it to the right of the rightmost x. """
lo, hi = 0, len(a) while lo < hi: mid = (lo+hi)//2 q += 1 less = input(f"{q:2}: IS {x:>6} LESS-THAN {a[mid]:>6} ? y/n: ").strip().lower() == 'y' if less: hi = mid else: lo = mid+1 a.insert(lo, x) return q
def order(items):
ordered, q = [], 0 for item in items: q = _insort_right(ordered, item, q) return ordered, q
if __name__ == '__main__':
items = 'violet red green indigo blue yellow orange'.split() ans, questions = order(items) print('\n' + ' '.join(ans))</lang>
- Output:
1: IS red LESS-THAN violet ? y/n: y 2: IS green LESS-THAN violet ? y/n: y 3: IS green LESS-THAN red ? y/n: n 4: IS indigo LESS-THAN green ? y/n: n 5: IS indigo LESS-THAN violet ? y/n: y 6: IS blue LESS-THAN indigo ? y/n: y 7: IS blue LESS-THAN green ? y/n: n 8: IS yellow LESS-THAN blue ? y/n: y 9: IS yellow LESS-THAN green ? y/n: y 10: IS yellow LESS-THAN red ? y/n: n 11: IS orange LESS-THAN blue ? y/n: y 12: IS orange LESS-THAN yellow ? y/n: y 13: IS orange LESS-THAN red ? y/n: n red orange yellow green blue indigo violet
Python: Sort with custom comparator
This uses a custom comparator together with functools.cmp_to_key to sort the previous order in fourteen questions.
<lang python>from functools import cmp_to_key
def user_cmp(a, b):
return int(input(f"IS {a:>6} <, ==, or > {b:>6} answer -1, 0 or 1:"))
if __name__ == '__main__':
items = 'violet red green indigo blue yellow orange'.split() ans = sorted(items, key=cmp_to_key(user_cmp)) print('\n' + ' '.join(ans))</lang>
- Output:
IS red <, ==, or > violet answer -1, 0 or 1:-1 IS green <, ==, or > red answer -1, 0 or 1:1 IS green <, ==, or > violet answer -1, 0 or 1:-1 IS green <, ==, or > red answer -1, 0 or 1:1 IS indigo <, ==, or > green answer -1, 0 or 1:1 IS indigo <, ==, or > violet answer -1, 0 or 1:-1 IS blue <, ==, or > indigo answer -1, 0 or 1:-1 IS blue <, ==, or > green answer -1, 0 or 1:1 IS yellow <, ==, or > blue answer -1, 0 or 1:-1 IS yellow <, ==, or > green answer -1, 0 or 1:-1 IS yellow <, ==, or > red answer -1, 0 or 1:1 IS orange <, ==, or > blue answer -1, 0 or 1:-1 IS orange <, ==, or > yellow answer -1, 0 or 1:-1 IS orange <, ==, or > red answer -1, 0 or 1:1 red orange yellow green blue indigo violet
Raku
Raku's sort (like most languages) can take a custom "comparator" routine. Since the calls to the comparator are minimized, and the info that the user provides is analogous to the required return values of the comparator, we just need to embed the prompt directly in the comparator.
<lang perl6>my $ask_count = 0; sub by_asking ( $a, $b ) {
$ask_count++; constant $fmt = '%2d. Is %-6s [ less than | greater than | equal to ] %-6s? ( < = > ) '; constant %o = '<' => Order::Less, '=' => Order::Same, '>' => Order::More;
loop { my $input = prompt sprintf $fmt, $ask_count, $a, $b; return $_ with %o{ $input.trim }; say "Invalid input '$input'"; }
}
my @colors = <violet red green indigo blue yellow orange>; my @sorted = @colors.sort: &by_asking; say (:@sorted);
die if @sorted».substr(0,1).join ne 'roygbiv'; my $expected_ask_count = @colors.elems * log(@colors.elems); warn "Too many questions? ({:$ask_count} > {:$expected_ask_count})" if $ask_count > $expected_ask_count;</lang>
- Output:
1. Is violet [ less than | greater than | equal to ] red ? ( < = > ) > 2. Is green [ less than | greater than | equal to ] indigo? ( < = > ) < 3. Is blue [ less than | greater than | equal to ] yellow? ( < = > ) > 4. Is red [ less than | greater than | equal to ] green ? ( < = > ) < 5. Is violet [ less than | greater than | equal to ] green ? ( < = > ) > 6. Is violet [ less than | greater than | equal to ] indigo? ( < = > ) > 7. Is yellow [ less than | greater than | equal to ] orange? ( < = > ) > 8. Is red [ less than | greater than | equal to ] orange? ( < = > ) < 9. Is green [ less than | greater than | equal to ] orange? ( < = > ) > 10. Is green [ less than | greater than | equal to ] yellow? ( < = > ) > 11. Is green [ less than | greater than | equal to ] blue ? ( < = > ) < 12. Is indigo [ less than | greater than | equal to ] blue ? ( < = > ) > sorted => [red orange yellow green blue indigo violet]
REXX
Extra code was added to the REXX program to handle incorrectly formatted answers.
Also note that lists in REXX start with unity, not zero. <lang>/*REXX pgm orders some items based on (correct) answers from a carbon─based life form. */ colors= 'violet red green indigo blue yellow orange'
q= 0; #= 0; $= do j=1 for words(colors); q= inSort( word(colors, j), q) end /*j*/ /*poise questions the CBLF about order.*/
say
do i=1 for #; say ' query' right(i, length(#) )":" !.i end /*i*/ /* [↑] show the list of queries to CBLF*/
say say 'final ordering: ' $ exit 0 /*──────────────────────────────────────────────────────────────────────────────────────*/ getAns: #= # + 1; _= copies('─', 8); y_n= ' Answer y/n'
do try=0 until ansU='Y' | ansU='N' if try>0 then say _ '(***error***) incorrect answer.' ask= _ ' is ' center(x,6) " less than " center(word($, mid+1),6) '?' say ask y_n; parse pull ans 1 ansU; ansU= space(ans); upper ansU end /*until*/; !.#= ask ' ' ans; return
/*──────────────────────────────────────────────────────────────────────────────────────*/ inSort: parse arg x, q; hi= words($); lo= 0
do q=q-1 while lo<hi; mid= (lo+hi) % 2 call getAns; if ansU=='Y' then hi= mid else lo= mid + 1 end /*q*/ $= subword($, 1, lo) x subword($, lo+1); return q</lang>
- output (only showing the results and eliding the querying/answering):
query 1: ──────── is red less than violet ? y query 2: ──────── is green less than violet ? y query 3: ──────── is green less than red ? n query 4: ──────── is indigo less than green ? n query 5: ──────── is indigo less than violet ? y query 6: ──────── is blue less than indigo ? y query 7: ──────── is blue less than green ? n query 8: ──────── is yellow less than blue ? y query 9: ──────── is yellow less than green ? y query 10: ──────── is yellow less than red ? n query 11: ──────── is orange less than blue ? y query 12: ──────── is orange less than yellow ? y query 13: ──────── is orange less than red ? n final ordering: red orange yellow green blue indigo violet
Wren
<lang ecmascript>import "/ioutil" for Input import "/fmt" for Fmt
// Inserts item x in list a, and keeps it sorted assuming a is already sorted. // If x is already in a, inserts it to the right of the rightmost x. var insortRight = Fn.new{ |a, x, q|
var lo = 0 var hi = a.count while (lo < hi) { var mid = ((lo + hi)/2).floor q = q + 1 var prompt = Fmt.swrite("$2d: Is $6s less than $6s ? y/n: ", q, x, a[mid]) var less = Input.option(prompt, "yn") == "y" if (less) { hi = mid } else { lo = mid + 1 } } a.insert(lo, x) return q
}
var order = Fn.new { |items|
var ordered = [] var q = 0 for (item in items) { q = insortRight.call(ordered, item, q) } return ordered
}
var items = "violet red green indigo blue yellow orange".split(" ") var ordered = order.call(items) System.print("\nThe colors of the rainbow, in sorted order, are:") System.print(ordered)</lang>
- Output:
1: Is red less than violet ? y/n: y 2: Is green less than violet ? y/n: y 3: Is green less than red ? y/n: n 4: Is indigo less than green ? y/n: n 5: Is indigo less than violet ? y/n: y 6: Is blue less than indigo ? y/n: y 7: Is blue less than green ? y/n: n 8: Is yellow less than blue ? y/n: y 9: Is yellow less than green ? y/n: y 10: Is yellow less than red ? y/n: n 11: Is orange less than blue ? y/n: y 12: Is orange less than yellow ? y/n: y 13: Is orange less than red ? y/n: n The colors of the rainbow, in sorted order, are: [red, orange, yellow, green, blue, indigo, violet]