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Word ladder

From Rosetta Code
Task
Word ladder
You are encouraged to solve this task according to the task description, using any language you may know.

Yet another shortest path problem. Given two words of equal length the task is to transpose the first into the second.

Only one letter may be changed at a time and the change must result in a word in unixdict, the minimum number of intermediate words should be used.

Demonstrate the following:

A boy can be made into a man: boy -> bay -> ban -> man

With a little more difficulty a girl can be made into a lady: girl -> gill -> gall -> gale -> gaze -> laze -> lazy -> lady

For the wokes, john can be made into jane: john -> cohn -> conn -> cone -> cane -> jane

A child can not be turned into an adult.

Optional transpositions of your choice.


Other tasks related to string operations:
Metrics
Counting
Remove/replace
Anagrams/Derangements/shuffling
Find/Search/Determine
Formatting
Song lyrics/poems/Mad Libs/phrases
Tokenize
Sequences



C++[edit]

This borrows heavily from Wren and a bit from Raku.

#include <algorithm>
#include <fstream>
#include <iostream>
#include <map>
#include <string>
#include <vector>
 
using word_map = std::map<size_t, std::vector<std::string>>;
 
// Returns true if strings s1 and s2 differ by one character.
bool one_away(const std::string& s1, const std::string& s2) {
if (s1.size() != s2.size())
return false;
bool result = false;
for (size_t i = 0, n = s1.size(); i != n; ++i) {
if (s1[i] != s2[i]) {
if (result)
return false;
result = true;
}
}
return result;
}
 
// Join a sequence of strings into a single string using the given separator.
template <typename iterator_type, typename separator_type>
std::string join(iterator_type begin, iterator_type end,
separator_type separator) {
std::string result;
if (begin != end) {
result += *begin++;
for (; begin != end; ++begin) {
result += separator;
result += *begin;
}
}
return result;
}
 
// Return true if v contains e.
template <typename vector_type, typename element_type>
bool contains(const vector_type& v, const element_type& e) {
return std::find(v.begin(), v.end(), e) != v.end();
}
 
// If possible, print the shortest chain of single-character modifications that
// leads from "from" to "to", with each intermediate step being a valid word.
// This is an application of breadth-first search.
bool word_ladder(const word_map& words, const std::string& from,
const std::string& to) {
auto w = words.find(from.size());
if (w != words.end()) {
auto poss = w->second;
std::vector<std::vector<std::string>> queue{{from}};
while (!queue.empty()) {
auto curr = queue.front();
queue.erase(queue.begin());
std::vector<std::string> next;
for (const std::string& str : poss) {
if (one_away(str, curr.back()))
next.push_back(str);
}
if (contains(next, to)) {
curr.push_back(to);
std::cout << join(curr.begin(), curr.end(), " -> ") << '\n';
return true;
}
poss.erase(std::remove_if(poss.begin(), poss.end(),
[&next](const std::string& str) {
return contains(next, str);
}),
poss.end());
for (const auto& str : next) {
std::vector<std::string> temp(curr);
temp.push_back(str);
queue.push_back(std::move(temp));
}
}
}
std::cout << from << " into " << to << " cannot be done.\n";
return false;
}
 
int main() {
word_map words;
std::ifstream in("unixdict.txt");
if (!in) {
std::cerr << "Cannot open file unixdict.txt.\n";
return EXIT_FAILURE;
}
std::string word;
while (getline(in, word))
words[word.size()].push_back(word);
word_ladder(words, "boy", "man");
word_ladder(words, "girl", "lady");
word_ladder(words, "john", "jane");
word_ladder(words, "child", "adult");
word_ladder(words, "cat", "dog");
word_ladder(words, "lead", "gold");
word_ladder(words, "white", "black");
word_ladder(words, "bubble", "tickle");
return EXIT_SUCCESS;
}
Output:
boy -> bay -> ban -> man
girl -> gill -> gall -> gale -> gaze -> laze -> lazy -> lady
john -> cohn -> conn -> cone -> cane -> jane
child into adult cannot be done.
cat -> cot -> cog -> dog
lead -> load -> goad -> gold
white -> whine -> chine -> chink -> clink -> blink -> blank -> black
bubble -> babble -> gabble -> garble -> gargle -> gaggle -> giggle -> jiggle -> jingle -> tingle -> tinkle -> tickle

F#[edit]

 
// Word ladder: Nigel Galloway. June 5th., 2021
let fG n g=n|>List.partition(fun n->2>Seq.fold2(fun z n g->z+if n=g then 0 else 1) 0 n g)
let wL n g=let dict=seq{use n=System.IO.File.OpenText("unixdict.txt") in while not n.EndOfStream do yield n.ReadLine()}|>Seq.filter(Seq.length>>(=)(Seq.length n))|>List.ofSeq|>List.except [n]
let (|Done|_|) n=n|>List.tryFind((=)g)
let rec wL n g l=match n with h::t->let i,e=fG l (List.head h) in match i with Done i->Some((i::h)|>List.rev) |_->wL t ((i|>List.map(fun i->i::h))@g) e
|_->match g with []->None |_->wL g [] l
let i,e=fG dict n in match i with Done i->Some([n;g]) |_->wL(i|>List.map(fun g->[g;n])) [] e
[("boy","man");("girl","lady");("john","jane");("child","adult")]|>List.iter(fun(n,g)->printfn "%s" (match wL n g with Some n->n|>String.concat " -> " |_->n+" into "+g+" can't be done"))
 
Output:
boy -> bay -> ban -> man
girl -> gill -> gall -> gale -> gaze -> laze -> lazy -> lady
john -> cohn -> conn -> cone -> cane -> jane
child into adult can't be done

Optional transpositions[edit]

The bad news is evil can not be turned into good, but the good news is god can become man.

 
[("evil","good");("god","man")]|>List.iter(fun(n,g)->printfn "%s" (match wL n g with Some n->n|>String.concat " -> " |_->n+" into "+g+" can't be done"))
 
Output:
evil into good can't be done done
god -> gad -> mad -> man

Go[edit]

Translation of: Wren
package main
 
import (
"bytes"
"fmt"
"io/ioutil"
"log"
"strings"
)
 
func contains(a []string, s string) bool {
for _, e := range a {
if e == s {
return true
}
}
return false
}
 
func oneAway(a, b string) bool {
sum := 0
for i := 0; i < len(a); i++ {
if a[i] != b[i] {
sum++
}
}
return sum == 1
}
 
func wordLadder(words []string, a, b string) {
l := len(a)
var poss []string
for _, word := range words {
if len(word) == l {
poss = append(poss, word)
}
}
todo := [][]string{{a}}
for len(todo) > 0 {
curr := todo[0]
todo = todo[1:]
var next []string
for _, word := range poss {
if oneAway(word, curr[len(curr)-1]) {
next = append(next, word)
}
}
if contains(next, b) {
curr = append(curr, b)
fmt.Println(strings.Join(curr, " -> "))
return
}
for i := len(poss) - 1; i >= 0; i-- {
if contains(next, poss[i]) {
copy(poss[i:], poss[i+1:])
poss[len(poss)-1] = ""
poss = poss[:len(poss)-1]
}
}
for _, s := range next {
temp := make([]string, len(curr))
copy(temp, curr)
temp = append(temp, s)
todo = append(todo, temp)
}
}
fmt.Println(a, "into", b, "cannot be done.")
}
 
func main() {
b, err := ioutil.ReadFile("unixdict.txt")
if err != nil {
log.Fatal("Error reading file")
}
bwords := bytes.Fields(b)
words := make([]string, len(bwords))
for i, bword := range bwords {
words[i] = string(bword)
}
pairs := [][]string{
{"boy", "man"},
{"girl", "lady"},
{"john", "jane"},
{"child", "adult"},
}
for _, pair := range pairs {
wordLadder(words, pair[0], pair[1])
}
}
Output:
boy -> bay -> ban -> man
girl -> gill -> gall -> gale -> gaze -> laze -> lazy -> lady
john -> cohn -> conn -> cone -> cane -> jane
child into adult cannot be done.

Java[edit]

import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.PriorityQueue;
import java.util.Set;
import java.util.stream.IntStream;
 
public class WordLadder {
private static int distance(String s1, String s2) {
assert s1.length() == s2.length();
return (int) IntStream.range(0, s1.length())
.filter(i -> s1.charAt(i) != s2.charAt(i))
.count();
}
 
private static void wordLadder(Map<Integer, Set<String>> words, String fw, String tw) {
wordLadder(words, fw, tw, 8);
}
 
private static void wordLadder(Map<Integer, Set<String>> words, String fw, String tw, int limit) {
if (fw.length() != tw.length()) {
throw new IllegalArgumentException("From word and to word must have the same length");
}
 
Set<String> ws = words.get(fw.length());
if (ws.contains(fw)) {
List<String> primeList = new ArrayList<>();
primeList.add(fw);
 
PriorityQueue<List<String>> queue = new PriorityQueue<>((chain1, chain2) -> {
int cmp1 = Integer.compare(chain1.size(), chain2.size());
if (cmp1 == 0) {
String last1 = chain1.get(chain1.size() - 1);
int d1 = distance(last1, tw);
 
String last2 = chain2.get(chain2.size() - 1);
int d2 = distance(last2, tw);
 
return Integer.compare(d1, d2);
}
return cmp1;
});
queue.add(primeList);
 
while (queue.size() > 0) {
List<String> curr = queue.remove();
if (curr.size() > limit) {
continue;
}
 
String last = curr.get(curr.size() - 1);
for (String word : ws) {
if (distance(last, word) == 1) {
if (word.equals(tw)) {
curr.add(word);
System.out.println(String.join(" -> ", curr));
return;
}
 
if (!curr.contains(word)) {
List<String> cp = new ArrayList<>(curr);
cp.add(word);
queue.add(cp);
}
}
}
}
}
 
System.err.printf("Cannot turn `%s` into `%s`%n", fw, tw);
}
 
public static void main(String[] args) throws IOException {
Map<Integer, Set<String>> words = new HashMap<>();
for (String line : Files.readAllLines(Path.of("unixdict.txt"))) {
Set<String> wl = words.computeIfAbsent(line.length(), HashSet::new);
wl.add(line);
}
 
wordLadder(words, "boy", "man");
wordLadder(words, "girl", "lady");
wordLadder(words, "john", "jane");
wordLadder(words, "child", "adult");
wordLadder(words, "cat", "dog");
wordLadder(words, "lead", "gold");
wordLadder(words, "white", "black");
wordLadder(words, "bubble", "tickle", 12);
}
}
Output:
boy -> bay -> may -> man
girl -> gill -> gall -> gale -> gaze -> laze -> lazy -> lady
john -> cohn -> conn -> cone -> cane -> jane
Cannot turn `child` into `adult`
cat -> cot -> dot -> dog
lead -> load -> goad -> gold
white -> whine -> chine -> chink -> clink -> blink -> blank -> black
bubble -> babble -> gabble -> garble -> gargle -> gaggle -> waggle -> wangle -> tangle -> tingle -> tinkle -> tickle

Julia[edit]

const dict = Set(split(read("unixdict.txt", String), r"\s+"))
 
function targeted_mutations(str::AbstractString, target::AbstractString)
working, tried = [[str]], Set{String}()
while all(a -> a[end] != target, working)
newworking = Vector{Vector{String}}()
for arr in working
s = arr[end]
push!(tried, s)
for j in 1:length(s), c in 'a':'z'
w = s[1:j-1] * c * s[j+1:end]
if w in dict && !(w in tried)
push!(newworking, [arr; w])
end
end
end
isempty(newworking) && return [["This cannot be done."]]
working = newworking
end
return filter(a -> a[end] == target, working)
end
 
println("boy to man: ", targeted_mutations("boy", "man"))
println("girl to lady: ", targeted_mutations("girl", "lady"))
println("john to jane: ", targeted_mutations("john", "jane"))
println("child to adult: ", targeted_mutations("child", "adult"))
 
Output:
boy to man: [["boy", "bay", "may", "man"], ["boy", "bay", "ban", "man"], ["boy", "bon", "ban", "man"]]
girl to lady: [["girl", "gill", "gall", "gale", "gaze", "laze", "lazy", "lady"]]
john to jane: [["john", "cohn", "conn", "cone", "cane", "jane"]]
child to adult: [["This cannot be done."]]

Mathematica / Wolfram Language[edit]

This example is incorrect. Please fix the code and remove this message.
Details: The requirement is to find the shortest path other examples do John to Jane with 4 intermediate words. Also an impossible example is required: child to adult.
db=DeleteDuplicates[RemoveDiacritics[ToLowerCase[Select[DictionaryLookup[],StringLength/*EqualTo[3]]]]];
sel=Select[Subsets[db,{2}],HammingDistance[#[[1]],#[[2]]]==1&];
g=Graph[db,[email protected]@@sel];
FindShortestPath[g,"boy","man"]
 
db=DeleteDuplicates[RemoveDiacritics[ToLowerCase[Select[DictionaryLookup[],StringLength/*EqualTo[4]]]]];
sel=Select[Subsets[db,{2}],HammingDistance[#[[1]],#[[2]]]==1&];
g=Graph[db,[email protected]@@sel];
FindShortestPath[g,"girl","lady"]
FindShortestPath[g,"john","jane"]
 
db=DeleteDuplicates[RemoveDiacritics[ToLowerCase[Select[DictionaryLookup[],StringLength/*EqualTo[5]]]]];
sel=Select[Subsets[db,{2}],HammingDistance[#[[1]],#[[2]]]==1&];
g=Graph[db,[email protected]@@sel];
FindShortestPath[g,"child","adult"]
Output:
{"boy", "bay", "ban", "man"}
{"girl", "gill", "gall", "gals", "gads", "lads", "lady"}
{"john", "join", "jain", "main", "mann", "mane", "jane"}
{}

Nim[edit]

import sets, strformat, strutils
 
 
func isOneAway(word1, word2: string): bool =
## Return true if "word1" and "word2" has only one letter of difference.
for i in 0..word1.high:
if word1[i] != word2[i]:
if result: return false # More than one letter of difference.
else: result = true # One letter of difference, for now.
 
var words: array[1..22, HashSet[string]] # Set of words sorted by length.
 
for word in "unixdict.txt".lines:
words[word.len].incl word
 
 
proc path(start, target: string): seq[string] =
## Return a path from "start" to "target" or an empty list
## if there is no possible path.
let lg = start.len
doAssert target.len == lg, "Source and destination must have same length."
doAssert start in words[lg], "Source must exist in the dictionary."
doAssert target in words[lg], "Destination must exist in the dictionary."
 
var currPaths = @[@[start]] # Current list of paths found.
var pool = words[lg] # List of possible words to use.
 
while true:
var newPaths: seq[seq[string]] # Next list of paths.
var added: HashSet[string] # Set of words added during the round.
for candidate in pool:
for path in currPaths:
if candidate.isOneAway(path[^1]):
let newPath = path & candidate
if candidate == target:
# Found a path.
return newPath
else:
# Not the target. Add a new path.
newPaths.add newPath
added.incl candidate
break
if newPaths.len == 0: break # No path.
currPaths = move(newPaths) # Update list of paths.
pool.excl added # Remove added words from pool.
 
 
when isMainModule:
for (start, target) in [("boy", "man"), ("girl", "lady"), ("john", "jane"),
("child", "adult"), ("cat", "dog"), ("lead", "gold"),
("white", "black"), ("bubble", "tickle")]:
let path = path(start, target)
if path.len == 0:
echo &"No path from “{start}” to “{target}”."
else:
echo path.join(" → ")
Output:
boy → bon → ban → man
girl → gill → gall → gale → gaze → laze → lazy → lady
john → cohn → conn → cone → cane → jane
No path from “child” to “adult”.
cat → cot → cog → dog
lead → load → goad → gold
white → whine → chine → chink → clink → clank → blank → black
bubble → babble → gabble → garble → gargle → gaggle → waggle → wangle → tangle → tingle → tinkle → tickle

Perl[edit]

Translation of: C++
use strict;
use warnings;
 
my %dict;
 
open my $handle, '<', 'unixdict.txt';
while (my $word = <$handle>) {
chomp($word);
my $len = length $word;
if (exists $dict{$len}) {
push @{ $dict{ $len } }, $word;
} else {
my @words = ( $word );
$dict{$len} = \@words;
}
}
close $handle;
 
sub distance {
my $w1 = shift;
my $w2 = shift;
 
my $dist = 0;
for my $i (0 .. length($w1) - 1) {
my $c1 = substr($w1, $i, 1);
my $c2 = substr($w2, $i, 1);
if (not ($c1 eq $c2)) {
$dist++;
}
}
return $dist;
}
 
sub contains {
my $aref = shift;
my $needle = shift;
 
for my $v (@$aref) {
if ($v eq $needle) {
return 1;
}
}
 
return 0;
}
 
sub word_ladder {
my $fw = shift;
my $tw = shift;
 
if (exists $dict{length $fw}) {
my @poss = @{ $dict{length $fw} };
my @queue = ([$fw]);
while (scalar @queue > 0) {
my $curr_ref = shift @queue;
my $last = $curr_ref->[-1];
 
my @next;
for my $word (@poss) {
if (distance($last, $word) == 1) {
push @next, $word;
}
}
 
if (contains(\@next, $tw)) {
push @$curr_ref, $tw;
print join (' -> ', @$curr_ref), "\n";
return;
}
 
for my $word (@next) {
for my $i (0 .. scalar @poss - 1) {
if ($word eq $poss[$i]) {
splice @poss, $i, 1;
last;
}
}
}
 
for my $word (@next) {
my @temp = @$curr_ref;
push @temp, $word;
 
push @queue, \@temp;
}
}
}
 
print STDERR "Cannot change $fw into $tw\n";
}
 
word_ladder('boy', 'man');
word_ladder('girl', 'lady');
word_ladder('john', 'jane');
word_ladder('child', 'adult');
word_ladder('cat', 'dog');
word_ladder('lead', 'gold');
word_ladder('white', 'black');
word_ladder('bubble', 'tickle');
Output:
boy -> bay -> ban -> man
girl -> gill -> gall -> gale -> gaze -> laze -> lazy -> lady
john -> cohn -> conn -> cone -> cane -> jane
Cannot change child into adult
cat -> cot -> cog -> dog
lead -> load -> goad -> gold
white -> whine -> chine -> chink -> clink -> blink -> blank -> black
bubble -> babble -> gabble -> garble -> gargle -> gaggle -> giggle -> jiggle -> jingle -> tingle -> tinkle -> tickle

Phix[edit]

with javascript_semantics
sequence words = unix_dict()

function right_length(string word, integer l) return length(word)=l end function

function one_away(string a, b) return sum(sq_ne(a,b))=1 end function

function dca(sequence s, n) return append(deep_copy(s),n) end function

procedure word_ladder(string a, b)
    sequence poss = filter(words,right_length,length(a)),
             todo = {{a}}, 
             curr -- aka todo[1], word chain starting from a
    while length(todo) do
        {curr,todo} = {todo[1],todo[2..$]}
        sequence next = filter(poss,one_away,curr[$])
        if find(b,next) then
            printf(1,"%s\n",{join(append(deep_copy(curr),b),"->")})
            return
        end if
        poss = filter(poss,"out",next)
        todo &= apply(true,dca,{{curr},next})
    end while
    printf(1,"%s into %s cannot be done\n",{a,b})
end procedure
word_ladder("boy","man")
word_ladder("girl","lady")
word_ladder("john","jane")
word_ladder("child","adult")

Aside: an initial poss = filter(poss,"out",{a}) might be prudent, but would only prevent a single next:={} step, at about the same cost as the initial filter anyway.

Output:
boy->bay->ban->man
girl->gill->gall->gale->gaze->laze->lazy->lady
john->cohn->conn->cone->cane->jane
child into adult cannot be done

Python[edit]

The function cache is not part of the algorithm but avoid re-download and map re-computing at each re-run.

import os,sys,zlib,urllib.request
 
def h ( str,x=9 ):
for c in str :
x = ( x*33 + ord( c )) & 0xffffffffff
return x
 
def cache ( func,*param ):
n = 'cache_%x.bin'%abs( h( repr( param )))
try  : return eval( zlib.decompress( open( n,'rb' ).read()))
except : pass
s = func( *param )
open( n,'wb' ).write( zlib.compress( bytes( repr( s ),'ascii' )))
return s
 
dico_url = 'https://raw.githubusercontent.com/quinnj/Rosetta-Julia/master/unixdict.txt'
read_url = lambda url  : urllib.request.urlopen( url ).read()
load_dico = lambda url  : tuple( cache( read_url,url ).split( b'\n'))
isnext = lambda w1,w2 : len( w1 ) == len( w2 ) and len( list( filter( lambda l : l[0]!=l[1] , zip( w1,w2 )))) == 1
 
def build_map ( words ):
map = [(w.decode('ascii'),[]) for w in words]
for i1,(w1,n1) in enumerate( map ):
for i2,(w2,n2) in enumerate( map[i1+1:],i1+1 ):
if isnext( w1,w2 ):
n1.append( i2 )
n2.append( i1 )
return map
 
def find_path ( words,w1,w2 ):
i = [w[0] for w in words].index( w1 )
front,done,res = [i],{i:-1},[]
while front :
i = front.pop(0)
word,next = words[i]
for n in next :
if n in done : continue
done[n] = i
if words[n][0] == w2 :
while n >= 0 :
res = [words[n][0]] + res
n = done[n]
return ' '.join( res )
front.append( n )
return '%s can not be turned into %s'%( w1,w2 )
 
for w in ('boy man','girl lady','john jane','alien drool','child adult'):
print( find_path( cache( build_map,load_dico( dico_url )),*w.split()))
Output:
boy bay ban man
girl gill gall gale gaze laze lazy lady
john cohn conn cone cane jane
alien alden alder alter aster ester eater bater bator baton baron boron moron moran moral morel monel money monty month mouth south sooth sloth slosh slash flash flask flank blank bland blend bleed breed bread tread triad trial trill drill droll drool
child can not be turned into adult

Racket[edit]

#lang racket
 
(define *unixdict* (delay (with-input-from-file "../../data/unixdict.txt"
(compose list->set port->lines))))
 
(define letters-as-strings (map string (string->list "abcdefghijklmnopqrstuvwxyz")))
 
(define ((replace-for-c-at-i w i) c)
(string-append (substring w 0 i) c (substring w (add1 i))))
 
(define (candidates w)
(for*/list (((i w_i) (in-parallel (string-length w) w))
(r (in-value (replace-for-c-at-i w i)))
(c letters-as-strings)
#:unless (char=? w_i (string-ref c 0)))
(r c)))
 
(define (generate-candidates word.path-hash)
(for*/hash (((w p) word.path-hash)
(w′ (candidates w)))
(values w′ (cons w p))))
 
(define (hash-filter-keys keep-key? h)
(for/hash (((k v) h) #:when (keep-key? k)) (values k v)))
 
(define (Word-ladder src dest (words (force *unixdict*)))
(let loop ((edge (hash src null)) (unused (set-remove words src)))
(let ((cands (generate-candidates edge)))
(if (hash-has-key? cands dest)
(reverse (cons dest (hash-ref cands dest)))
(let ((new-edge (hash-filter-keys (curry set-member? unused) cands)))
(if (hash-empty? new-edge)
`(no-path-between ,src ,dest)
(loop new-edge (set-subtract unused (list->set (hash-keys new-edge))))))))))
 
(module+ main
(Word-ladder "boy" "man")
(Word-ladder "girl" "lady")
(Word-ladder "john" "jane")
(Word-ladder "alien" "drool")
(Word-ladder "child" "adult"))
Output:
'("boy" "bay" "may" "man")
'("girl" "gill" "gall" "gale" "gaze" "laze" "lazy" "lady")
'("john" "cohn" "conn" "cone" "cane" "jane")
'("alien"
  "alden"
  "alder"
  "alter"
  "aster"
  "ester"
  "eater"
  "bater"
  "bator"
  "baton"
  "baron"
  "boron"
  "moron"
  "moran"
  "moral"
  "morel"
  "monel"
  "money"
  "monty"
  "month"
  "mouth"
  "south"
  "sooth"
  "sloth"
  "slosh"
  "slash"
  "flash"
  "flask"
  "flank"
  "blank"
  "bland"
  "blend"
  "bleed"
  "breed"
  "bread"
  "tread"
  "triad"
  "trial"
  "trill"
  "drill"
  "droll"
  "drool")
'(no-path-between "child" "adult")

Raku[edit]

constant %dict = 'unixdict.txt'.IO.lines
.classify(*.chars)
.map({ .key => .value.Set });
 
sub word_ladder ( Str $from, Str $to ) {
die if $from.chars != $to.chars;
 
my $sized_dict = %dict{$from.chars};
 
my @workqueue = (($from,),);
my $used = ($from => True).SetHash;
while @workqueue {
my @new_q;
for @workqueue -> @words {
my $last_word = @words.tail;
my @new_tails = gather for 'a' .. 'z' -> $replacement_letter {
for ^$last_word.chars -> $i {
my $new_word = $last_word;
$new_word.substr-rw($i, 1) = $replacement_letter;
 
next unless $new_word$sized_dict
and not $new_word$used;
take $new_word;
$used{$new_word} = True;
 
return |@words, $new_word if $new_word eq $to;
}
}
push @new_q, ( |@words, $_ ) for @new_tails;
}
@workqueue = @new_q;
}
}
for <boy man>, <girl lady>, <john jane>, <child adult> -> ($from, $to) {
say word_ladder($from, $to)
// "$from into $to cannot be done";
}
Output:
(boy bay may man)
(girl gill gall gale gaze laze lazy lady)
(john cohn conn cone cane jane)
child into adult cannot be done

REXX[edit]

This REXX entry does a little more error checking.

It also assumes that the dictionary file is in mixed case as well as the words entered on the CL.

To treat the dictionary and input words as caseless,   all words are translated to lowercase.

Programming note:     this REXX program uses the   lower   BIF   which Regina has).
If your REXX doesn't support that BIF,   here is an equivalent function:

lower: procedure;  parse arg a;   @= 'abcdefghijklmnopqrstuvwxyz';    @u= @;    upper @u
return translate(a, @, @u)
/*REXX program finds words  (within an identified dict.)  to solve a word ladder puzzle.*/
parse arg base targ iFID . /*obtain optional arguments from the CL*/
if base=='' | base=="," then base= 'boy' /*Not specified? Then use the default.*/
if targ=='' | targ=="," then targ= 'man' /* " " " " " " */
if iFID=='' | iFID=="," then iFID='unixdict.txt' /* " " " " " " */
abc= 'abcdefghijklmnopqrstuvwxyz' /*the lowercase (Latin) alphabet. */
abcU= abc; upper abcU /* " uppercase " " */
base= lower(base); targ= lower(targ) /*lowercase the BASE and also the TARG.*/
L= length(base) /*length of the BASE (in characters). */
if L<2 then call err 'base word is too small or missing' /*oops, too small*/
if length(targ)\==L then call msg , "target word isn't the same length as the base word"
call letters /*assign letters, faster than SUBSTR. */
#= 0 /*# of words whose length matches BASE.*/
@.= /*default value of any dictionary word.*/
do recs=0 while lines(iFID)\==0 /*read each word in the file (word=X).*/
x= lower(strip( linein( iFID) ) ) /*pick off a word from the input line. */
if length(x)\==L then iterate /*Word not correct length? Then skip. */
#= # + 1; @.x= 1 /*bump # words with length L; semaphore*/
end /*recs*/ /* [↑] semaphore name is uppercased. */
!.= 0
say copies('─', 30) recs "words in the dictionary file: " iFID
say copies('─', 30) # "words in the dictionary file of length: " L
say copies('─', 30) ' base word is: ' base
say copies('─', 30) 'target word is: ' targ
rung= targ
$= base
do f=1 for m; call look; if result\=='' then leave /*Found? Quit.*/
end /*f*/
say
if f>m then call msg 'no word ladder solution possible for ' base " ──► " targ
 
do f-2; $= base;  !.= 0 /*process all the rungs that were found*/
do forever; call look; if result\=='' then leave /*Found? Quit.*/
end /*forever*/
end /*f-2*/
call show words(rung)
exit 0 /*stick a fork in it, we're all done. */
/*──────────────────────────────────────────────────────────────────────────────────────*/
msg: say; if arg()==2 then say '***error*** ' arg(2); else say arg(1); say; exit 13
show: say 'a solution: ' base; do j=1 to arg(1); say left('',12) word(rung,j); end; return
letters: do m=1 for length(abc); a.m= substr(abc, m, 1); end; return
/*──────────────────────────────────────────────────────────────────────────────────────*/
look: procedure expose @. !. a. $ abc base L rung targ search; rungs= word(rung, 1)
$$=; rung#= words(rungs)
do i=1 for words($); y= word($, i);  !.y= 1
do k=1 for L
do n=1 for 26; z= overlay(a.n, y, k) /*change a letter*/
if @.z=='' then iterate /*Is this not a word? Then skip it. */
if !.z then iterate /* " " a repeat? " " " */
if z==rungs then rung= y rung /*prepend a word to the rung list. */
if z==rungs & rung#>1 then return z /*short─circuit. */
if z==targ then return z
$$= $$ z /*append a possible ladder word to $$*/
end /*n*/
end /*k*/
end /*i*/
$= $$; return ''
output   when using the default inputs:
────────────────────────────── 25104 words in the dictionary file:  unixdict.txt
────────────────────────────── 796 words in the dictionary file of length:  3
──────────────────────────────  base  word is:  boy
────────────────────────────── target word is:  man

a solution:  boy
             bay
             may
             man
output   when using the inputs of:     girl   lady
────────────────────────────── 25104 words in the dictionary file:  unixdict.txt
────────────────────────────── 2187 words in the dictionary file of length:  4
──────────────────────────────  base  word is:  girl
────────────────────────────── target word is:  lady

a solution:  girl
             gill
             gall
             gale
             gaze
             laze
             lazy
             lady
output   when using the inputs of:     john   jane
────────────────────────────── 25104 words in the dictionary file:  unixdict.txt
────────────────────────────── 2187 words in the dictionary file of length:  4
──────────────────────────────  base  word is:  john
────────────────────────────── target word is:  jane

a solution:  john
             cohn
             conn
             cone
             cane
             jane
output   when using the inputs of:     child   adult
────────────────────────────── 25104 words in the dictionary file:  unixdict.txt
────────────────────────────── 3161 words in the dictionary file of length:  5
──────────────────────────────  base  word is:  child
────────────────────────────── target word is:  adult

no word ladder solution possible for  child  ──►  adult

Swift[edit]

Translation of: Wren
import Foundation
 
func oneAway(string1: String, string2: String) -> Bool {
if string1.count != string2.count {
return false
}
var result = false
for (c1, c2) in zip(string1, string2) {
if c1 != c2 {
if result {
return false
}
result = true
}
}
return result
}
 
func wordLadder(words: [String], from: String, to: String) {
var poss = words.filter{$0.count == from.count}
var queue: [[String]] = [[from]]
while !queue.isEmpty {
var curr = queue[0]
let last = curr[curr.count - 1]
queue.removeFirst()
let next = poss.filter{oneAway(string1: $0, string2: last)}
if next.contains(to) {
curr.append(to)
print(curr.joined(separator: " -> "))
return
}
poss.removeAll(where: {next.contains($0)})
for str in next {
var temp = curr
temp.append(str)
queue.append(temp)
}
}
print("\(from) into \(to) cannot be done.")
}
 
do {
let words = try String(contentsOfFile: "unixdict.txt", encoding: String.Encoding.ascii)
.components(separatedBy: "\n")
.filter{!$0.isEmpty}
wordLadder(words: words, from: "man", to: "boy")
wordLadder(words: words, from: "girl", to: "lady")
wordLadder(words: words, from: "john", to: "jane")
wordLadder(words: words, from: "child", to: "adult")
} catch {
print(error.localizedDescription)
}
Output:
man -> ban -> bay -> boy
girl -> gill -> gall -> gale -> gaze -> laze -> lazy -> lady
john -> cohn -> conn -> cone -> cane -> jane
child into adult cannot be done.

Wren[edit]

Translation of: Phix
Library: Wren-sort
import "io" for File
import "/sort" for Find
 
var words = File.read("unixdict.txt").trim().split("\n")
 
var oneAway = Fn.new { |a, b|
var sum = 0
for (i in 0...a.count) if (a[i] != b[i]) sum = sum + 1
return sum == 1
}
 
var wordLadder = Fn.new { |a, b|
var l = a.count
var poss = words.where { |w| w.count == l }.toList
var todo = [[a]]
while (todo.count > 0) {
var curr = todo[0]
todo = todo[1..-1]
var next = poss.where { |w| oneAway.call(w, curr[-1]) }.toList
if (Find.first(next, b) != -1) {
curr.add(b)
System.print(curr.join(" -> "))
return
}
poss = poss.where { |p| !next.contains(p) }.toList
for (i in 0...next.count) {
var temp = curr.toList
temp.add(next[i])
todo.add(temp)
}
}
System.print("%(a) into %(b) cannot be done.")
}
 
var pairs = [
["boy", "man"],
["girl", "lady"],
["john", "jane"],
["child", "adult"]
]
for (pair in pairs) wordLadder.call(pair[0], pair[1])
Output:
boy -> bay -> ban -> man
girl -> gill -> gall -> gale -> gaze -> laze -> lazy -> lady
john -> cohn -> conn -> cone -> cane -> jane
child into adult cannot be done.