Updated 2016-05-03 19:33:30 by gold

Keith Vetter 2006-10-12 : Here's a little program to solve word chains--a list of words where each word differs from its neighbor by exactly one letter. An example of a word chain would be warm - ward - card - cord - cold.

You first enter a starting and ending word both of either three or four letters. Then this program will compute the shortest word chain leading from the starting word and leading to the ending word. Built into this program is a 500+ 3-letter word list and a 2300+ 4-letter word list.

I'm a bit proud of my algorithm for determining all neighboring words for given word. I came up with a 1-liner using regular expressions and lsearch. For example, the neighbors of warm can be found with:
    lsearch -all -regexp $wordlist "(.arm)|(w.rm)|(wa.m)|(war.)"

See also The word-chain game for an abortive start at a similar idea.
 # WordChain.tcl -- Computes word chains for 3 & 4 letter words
 # by Keith Vetter, Oct 12, 2006 
 package require Tk
 package require tile
 proc DoDisplay {} {
    wm title . "Word Chain"
    label .title -text "Word Chain" -font {Times 32 bold} -relief raised -fg blue
    frame .puzzle 
    entry .start -textvariable W(start) -width 5
    label .arrow -text ">>"
    entry .end -textvariable W(end) -width 5
    frame .answer -bd 2 -relief ridge
    listbox .lb -yscrollcommand ".sb_y set" -bd 0 -listvariable W(answer) \
        -exportselection 0 -takefocus 0 -font {Courier 10} -width 11 -height 9
    scrollbar .sb_y -orient v -command ".lb yview"
    pack .sb_y -in .answer -side right -fill y
    pack .lb -in .answer -side left -fill both -expand 1
    pack .answer -in .puzzle -side bottom -pady {10 0}
    pack .start .arrow .end -in .puzzle -side left -expand 1
    frame .buttons
    ::ttk::button .go -text "Solve" -command Solve
    ::ttk::button .rand -text "Random" -command Random
    ::ttk::button .about -text About -command About
    pack .go .rand -in .buttons -side top -padx 10 -pady 5
    pack .about -side bottom -in .buttons
    grid .title - -pady 10 -padx 10 -ipadx 10
    grid .puzzle .buttons -sticky ns -pady {0 10}
    foreach i [trace info variable ::W] { eval trace remove variable ::W $i }
    set ::W(solving) 0
    trace variable ::W w Tracer
 proc Chain {start end {progress {}}} {
    if {$start eq $end} {return [list $start $end]}
    set wlen [string length $start]
    QPush [list $start -1 0]
    QVisited $start
    set cnt 0
    while {1} {
        foreach {id word . depth} [QPop] break
        if {$id == -1} break                    ;# Failure, empty Q
        incr depth
        if {([incr cnt] % 100) == 0} {
            if {$progress ne ""} { $progress $cnt $depth }
        foreach idx [lsearch -all -regexp $::WORDS($wlen) [MakeRE $word]] {
            set next [lindex $::WORDS($wlen) $idx]
            if {[QVisited $next]} continue      ;# Already done this word, skip
            QPush [list $next $id $depth]
            if {$next eq $end} break
        if {$next eq $end} break
    if {$id == -1} { return {} }
    return [GetSolution]
 proc Progress {cnt depth} {
    lappend ::W(answer) [format "%2d %5d" $depth $cnt]
    .lb see end
 proc MakeRE {word} {
    set re {}
    for {set i 0} {$i < [string length $word]} {incr i} {
        lappend re "([string replace $word $i $i .])"
    set re [join $re "|"]
    return $re
 proc QInit {} {
    unset -nocomplain ::Q
    set ::Q(head) 0                             ;# Head: 1 ahead of first item
    set ::Q(tail) 0                             ;# Tail: last unviewed item
 proc QPush {token} {
    set ::Q($::Q(head)) $token
    incr ::Q(head)
 proc QPop {} {
    if {$::Q(head) == $::Q(tail)} { return -1}  ;# Empty Q
    set id $::Q(tail)
    incr ::Q(tail)
    return [concat $id $::Q($id)]
 proc QVisited {word} {
    if {[info exists ::Q(v,$word)]} { return 1 }
    set ::Q(v,$word) 1
    return 0
 proc GetSolution {} {
    set id [expr {$::Q(head) - 1}]              ;# Last item in Q
    set chain {}
    while {$id != -1} {
        foreach {word id} $::Q($id) break
        set chain [concat $word $chain]
    return $chain
 proc Shuffle { alist } {
    set len [llength $alist]
    set len2 $len
    for {set i 0} {$i < $len-1} {incr i} {
        set n [expr {int($i + $len2 * rand())}]
        incr len2 -1
        # Swap elements at i & n
        set temp [lindex $alist $i]
        lset alist $i [lindex $alist $n]
        lset alist $n $temp
    return $alist
 proc Solve {} {
    if {$::W(solving)} return

    set ::WORDS(3) [Shuffle $::WORDS(3)]
    set ::WORDS(4) [Shuffle $::WORDS(4)]

    set ::W(solving) 1
    set ::W(answer) "Solving..."
    set answer [Chain $::W(start) $::W(end) Progress]
    if {$answer eq ""} {set answer impossible}
    set ::W(answer) $answer
    set ::W(solving) 0
 proc Random {} {
    if {$::W(solving)} return
    set wlen [expr {rand() > .5 ? 4 : 3}]
    set llen [llength $::WORDS($wlen)]
    set ::W(start) [lindex $::WORDS($wlen) [expr {int(rand() * $llen)}]]
    set ::W(end) [lindex $::WORDS($wlen) [expr {int(rand() * $llen)}]]
    set ::W(answer) ""
 proc Tracer {var1 var2 op} {
    if {$::W(solving)} return
    set status disabled
    while {1} {
        set wlen [string length $::W(start)]
        if {$wlen != [string length $::W(end)]} break
        if {! [info exists ::WORDS($wlen)]} break
        if {[lsearch -exact $::WORDS($wlen) $::W(start)] == -1} break
        if {[lsearch -exact $::WORDS($wlen) $::W(end)] == -1} break
        set status normal
    .go config -state $status
 proc About {} {
    set msg "Word Chain\nBy Keith Vetter, Oct 2006"
    tk_messageBox -title "About" -message $msg
 set WORDS(3) {
    ace act add ade ado ads adz aft age ago aha aid ail aim air alb ale all alp
    amp and ant any ape apt arc are ark arm art ash ask asp ass ate auf aux awe
    awl awn axe aye baa bad bag bah ban bar bat bay bed bee beg bet bib bid big
    bin bit boa bob bog boo bop bow box boy bra bud bug bum bun bus but buy bye
    cab cad cam can cap car cat caw cay cee chi cob cod cog col con coo cop cot
    cow coy cry cub cud cue cup cur cut dab dad dam day dee den dew did die dig
    dim din dip doc doe dog don dot dry dub dud due dug dun duo dye ear eat ebb
    eel egg ego eke elf elk ell elm emu end eon era ere erg err eta eve ewe eye
    fad fag fan far fat fax fay fed fee fen few fey fez fib fie fig fin fir fit
    fix flu fly fob foe fog fop for fox fro fry fun fur gab gad gag gal gam gap
    gar gas gay gee gel gem get gig gin gnu gob god got gum gun gut guy gym gyp
    had hag hah ham has hat haw hay hem hen hep her hew hex hey hid hie him hip
    his hit hob hod hoe hog hoi hop hot how hub hue hug huh hum hut ice icy ifs
    ilk ill imp ink inn ins ion ire irk its ivy jab jag jam jar jaw jay jet jib
    jig job jog jot joy jug jus jut keg ken key kid kin kip kit lab lad lag lam
    lap law lax lay lea led lee leg lei let lib lid lie lip lit lob log loo lop
    lot low lox lug lye mad man map mar mat maw max may men met mew mid mil min
    mix mob mod mom moo mop mow mud mug mum nab nag nap nay nee net new nib nil
    nip nit nix nod non nor not now nth nub nun nut oaf oak oar oat obi odd ode
    off oft ohm oil old ole one opt orb ore ort our out ova owe owl own pad pal
    pan pap par pat paw pay pea pee peg pen pep per pet pew phi pie pig pin pip
    pit pix ply pod poi pop pot pow pox pry psi pub pug pun pup pus put rag rah
    ram ran rap rat raw ray red ref rep ret rev rex rho rib rid rig rim rip rob
    roc rod roe rot row rub rue rug rum run rut rye sac sad sag sap sat saw sax
    say sea see seq set sew sex she shy sic sin sip sir sis sit six ski sky sly
    sob sod sol son sop sot sow soy spa spy sty sub sue sum sun sup tab tad tag
    tam tan tao tap tar tat tau tax tea ted tee ten the thy tic tie tin tip tit
    toe tog tom ton too top tor tot tow toy try tub tug tun tux two ump ups urn
    use van vat vee vet vex via vie vim viz vow wad wag wan war was wax way web
    wed wee wet who why wig win wit woe won woo wow wry yak yam yap yaw yea yen
    yes yet yew yip yon you zag zap zed zee zip zoo}
 set WORDS(4) {
    abbe abed abet able ably abut aced aces ache achy acid acme acne acre acts
    acyl adds aero afar agar aged ages agog ague ahem ahoy aide aids ails aims
    airs airy ajar akin alai alar alas alba albs alee ales alga alia alit ally
    alms aloe alps also alto alum amah ambo amen amid ammo amok amps anal anew
    ankh anon ante ants anus aped apes apex apse aqua arch arcs area ares aria
    arid arks arms army arts arty arum ashy asks asps assn atom atop aula auld
    aunt aura auto avec aver avid avis avow away awed awes awls awns awry axed
    axes axil axis axle axon ayah ayes baas babe baby back bade bags bail bait
    bake bald bale balk ball balm band bane bang bank bans barb bard bare bark
    barn bars base bash bask bass bate bath bats batt baud bawd bawl bays bead
    beak beam bean bear beat beau beck beds beef been beep beer bees beet begs
    bell belt bema bend bent berg best beta bets bevy bias bibs bide bids bier
    bike bile bilk bill bind bins bird bite bits blab bled blew blip blob bloc
    blot blow blue blur boar boas boat bobs bock bode body bogs bogy boil bola
    bold bole boll bolo bolt bomb bona bond bone bong bony book boom boon boor
    boos boot bops bore born bosh boss both bout bowl bows boxy brad brae brag
    bran bras brat bray bred brew brig brim brow brut bubo buck buds buff bugs
    bulb bulk bull bump bums bung bunk buns bunt buoy burg burl burn burp burr
    bury bush buss bust busy butt buys buzz byes byte cabs cads cafe cage cake
    calf call calm came camp cams cane cans cant cape caps card care carp cars
    cart case cash cask cast cats cava cave cavy caws cays cede cell cent chap
    char chat chef chew chic chin chip chit chop chow chub chug chum ciao cite
    city clad clam clan clap claw clay clef clew clip clod clog clop clot cloy
    club clue coal coat coax cobs coca cock coco coda code cods coed cogs coif
    coil coin coke cola cold colt coma comb come cone conk conn cons cony cook
    cool coon coop coos coot cope cops copy cord core cork corn cost cote cots
    coup cove cowl cows cozy crab crag cram crap craw crew crib crop crow crux
    cube cubs cuds cued cues cuff cull cult cups curb curd cure curl curs curt
    cusp cuss cute cuts cyan cyst czar dabs dado dads daft dais dale dame damn
    damp dams dank dare dark darn dart dash data date daub dawn days daze dead
    deaf deal dean dear debt deck deed deem deep deer deft defy deja deli dell
    demo dens dent deny desk dewy dhow dial dice dick died diem dies diet digs
    dike dill dime dims dine ding dins dint dips dire dirk dirt disc dish disk
    diva dive dock docs dodo doer does doff doge dogs dole doll dolt dome done
    dong dons doom door dope dorm dory dose dost dote doth dots dour dove down
    doze dozy drab drag dram draw dray drew drip drop drub drug drum dual dubs
    duck duct dude duds duel dues duet dugs duke dull duly dumb dump dune dung
    dunk duns duos dupe dusk dust duty dyad dyed dyer dyes dyne each earl earn
    ears ease east easy eats eave ebbs echo ecru eddy edge edgy edit eels egad
    eggs egos eked ekes elan elks ells elms else emir emit emus ends envy eons
    epee epic eras ergo ergs errs espy etch even ever eves evil ewer ewes exam
    exec exes exit eyed face fact fade fads fags fail fair fake fall fame fang
    fans fare farm faro fast fate fats faun faux fawn fays faze fear feat feed
    feel fees fell felt fend fens fern fete feud fiat fibs fife figs file fill
    film find fine fink fins fire firm firs fish fist fits five fizz flag flak
    flap flat flaw flax flay flea fled flee flew flex flip flit floc floe flog
    flop flow flub flue flux foal foam fobs foci foes fogs fogy foil fold folk
    fond font food fool foot fops ford fore fork form fort foul four fowl foxy
    frau fray free fret frog from fuel full fume fumy fund funk furl furs fury
    fuse fuss fuzz gabs gads gaff gage gags gain gait gala gale gall gals game
    gams gamy gang gape gaps garb gars gash gasp gate gaud gave gawk gays gaze
    gear geek geld gels gems gene gent germ gets gibe gift gigs gild gill gilt
    gins gird girl girt gist give glad glee glen glib glob glow glue glum glut
    gnat gnaw gnus goad goal goat gobs gods goes gogo gold golf gone gong good
    goof gook goon gore gory gosh gout gown grab grad gram gray grew grey grid
    grim grin grip grit grog grot grow grub gulf gull gulp gums gunk guns guru
    gush gust guts guys gyms gyps gyre gyro hack haft hags hail hair hake hale
    half hall halo halt hams hand hang hank hard hare hark harm harp hart hash
    hasp hast hate hath hats haul have hawk haws hays haze hazy head heal heap
    hear heat heck heed heel heft heir held hell helm help hemp hems hens herb
    herd here hero hers hewn hews hick hide hied hies high hike hill hilt hind
    hint hips hire hiss hits hive hoax hobo hobs hock hods hoed hoer hoes hogs
    hold hole holy home homo hone honk hood hoof hook hoop hoot hope hops horn
    hors hose host hour hove howl hubs huck hued hues huff huge hugs hula hulk
    hull hump hums hung hunk hunt hurl hurt hush husk huts hymn hypo iamb ibex
    ibid ibis iced ices icon idea ides idle idly idol iffy ills imam imps inch
    info inks inky inns into ions iota ipso ires iris irks iron isle itch item
    jabs jack jade jags jail jake jamb jams jape jars jaws jays jazz jean jeep
    jeer jell jerk jess jest jets jibe jibs jiff jigs jilt jinn jinx jive jobs
    jock jogs john joie join joke jolt josh joss jots jour jowl joys judo jugs
    jump junk jure jury just jute juts kale kava kayo keel keen keep kegs kelp
    kens kepi kept keys khan kick kids kill kiln kilo kilt kind kine king kink
    kips kirk kiss kite kith kits kiwi knee knew knit knob knot know kola kung
    labs lace lack lacy lade lads lady lags laid lain lair lake laky lama lamb
    lame lamp land lane lank laps lard lark lash lass last late lath laud lava
    lave lawn laws lays laze lazy lead leaf leak lean leap leas leek leer lees
    left legs leis lend lens lent less lest lets levy lewd liar libs lice lice
    lick lids lied lief lien lies lieu life lift like lilt lily limb lime limn
    limp limy line ling link lint lion lips lisp list live load loaf loam loan
    lobe lobs loch loci lock loco lode loft loge logs logy loin loll lone long
    look loom loon loop loot lope lops lord lore lose loss lost lots loud lout
    love lows lube luck luff lugs lull lump lung lure lurk lush lust lute lyes
    lynx lyre mace made magi maid mail maim main make male mall malt mama mane
    mans many maps mare mark marl mars mart mash mask mass mast mate math mats
    maul maws maze mazy mead meal mean meat meed meek meet meld melt memo mend
    menu mere mesa mesh mess mete mewl mews mica mice midi mien miff migs mike
    mild mile milk mill mils milt mime mind mine mini mink mins mint minx mire
    miry miss mist mite mitt moan moat mobs mock mode moil mold mole moll molt
    moms monk mono mood moon moor moos moot mope mops more morn moss most mote
    moth move mown mows much muck muff mugs mule mull mums murk muse mush musk
    muss must mute mutt myna myth nabs nags nail name nape naps nard nary nave
    navy nays neap near neat nebs neck need neon nest nets news newt next nibs
    nice nick nigh nine nips nits node nods noel nolo none nons nook noon nope
    norm nose nosy note noun nova nubs nude nuke null numb nuns nuts oafs oaks
    oars oath oats obey oboe odds odes odor offs ogle ogre ohms oils oily oink
    okay okra oleo olio omen omit once ones only onto onus onyx ooze oozy opal
    open opts opus oral orbs ores orgy orts otic ouch ours oust outs ouzo oval
    oven over ovum owed owes owls owns oxen pace pack pact pads page paid pail
    pain pair pale pall palm pals pane pang pans pant papa pare park pars part
    pass past pate path pats pave pawl pawn paws pays peak peal pear peas peat
    peck peek peel peen peep peer pees pegs pelf pelt pend pens pent peon peps
    perk perm pert peso pest pets pews pica pick pied pier pies pigs pike pile
    pill pimp pine ping pink pins pint pipe pips pita pith pits pity pixy plan
    plat play plea pled plod plop plot plow ploy plug plum plus pock pods poem
    poet poke poky pole poll polo poly pomp pond pony pooh pool poop poor pope
    pops pore pork port pose posh post posy pots pour pout pows pram pray prep
    prey prig prim prix prod prof prom prop prow pubs puce puck puff pugs puke
    pull pulp puma pump punk puns punt puny pupa pups pure purl purr push puss
    puts putt pyre quad quay quid quip quit quiz race rack racy raft raga rage
    rags raid rail rain raja rake ramp rams rang rank rant rape raps rapt rare
    rash rasp rate rats rave rays raze razz read real ream reap rear redo reds
    reed reef reek reel refs rein rely rend rent rest rets revs rhea ribs rice
    rich rick ride rids rife riff rift rigs rile rill rime rims rind ring rink
    riot ripe rips rise risk rite rive road roam roan roar robe robs rock rocs
    rode rods roes roil role roll romp rood roof rook room root rope rose rosy
    rote rots rout rove rows rube rubs ruby rude rued rues ruff rugs ruin rule
    rump rums rune rung runs runt ruse rush rusk rust ruts ryes sack sacs safe
    saga sage sago sags said sail sake sale salt same sand sane sang sank sans
    saps sari sash sass sate save sawn saws says scab scam scan scar scat scow
    scud scum seal seam sear seas seat sect seed seek seem seen seep seer sees
    self sell semi send sent sera sere serf seta sets sewn sews sexy shad shag
    shah sham shaw shay shed shim shin ship shiv shod shoe shoo shop shot show
    shun shut sick side sift sigh sign silk sill silo silt sine sing sink sins
    sips sire sirs site sits size skew skid skim skin skip skis skit slab slag
    slam slap slat slaw slay sled slew slid slim slip slit slob sloe slog slop
    slot slow slue slug slum slur slut smog smug smut snag snap snip snob snot
    snow snub snug soak soap soar sobs sock soda sods sofa soft soil sold sole
    solo sols some song sons soon soot sops sore sort sots soul soup sour sown
    sows soya span spar spas spat spay spec sped spew spin spit spot spry spud
    spun spur stab stag star stay stem step stet stew stir stop stow stub stud
    stun subs such suck suds sued sues suet suey suit sulk sums sung sunk suns
    sups sure surf swab swag swam swan swap swat sway swig swim swum sync tabs
    tabu tack tact tads taft tags tail take talc tale talk tall tame tamp tams
    tang tank tans tape taps tare tarn taro tarp tars tart task tats taut taxi
    teak teal team tear teas teat tech teds teed teem teen tees tell temp tend
    tens tent term tern test text than that thaw thee them then they thin this
    thou thud thug thus tick tics tide tidy tied tier ties tiff tile till tilt
    time tine tins tint tiny tips tire tits toad toed toes tofu toga togs toil
    toke told toll tomb tome toms tone tong tonk tons took tool toot tope tops
    tore torn tort toss tote tots tour tout town tows toys tram trap tray tree
    trek trig trim trio trip trod trot troy true tsar tuba tube tubs tuck tufa
    tuff tuft tugs tuna tune tung tuns turf turn tusk tutu twig twin twit twos
    tyke type typo tyro ugly ulna umps undo unit unto upon urea urge uric urns
    used user uses vade vain vale vamp vane vans vary vase vast vats veal veer
    vees veil vein vela vend vent verb very vest veto vets vial vice vied vies
    view vile vine viol visa vise vita viva vive vivo void vole volt vote vows
    wade wadi wads waft wage wags waif wail wait wake walk wall wand wane want
    ward ware warm warn warp wars wart wary wash wasp watt wave wavy waxy ways
    weak weal wean wear webs weds weed week weep weft weir weld well welt wend
    went wept were wert west wets wham what when whet whew whey whim whip whir
    whit whiz whoa whom whys wick wide wife wigs wild wile will wilt wily wind
    wine wing wink wins winy wipe wire wiry wise wish wisp with wits wive woad
    woes woke wold wolf womb wont wood woof wool woos word wore work worm worn
    wove wows wrap wren writ yaks yams yang yank yaps yard yarn yawl yawn yawp
    yaws yeah year yegg yell yelp yens yews yips yoga yogi yoke yolk yore your
    yowl yule yurt zany zaps zeal zebu zero zest zeta zinc zing zips zone zoom}
 set start amen
 set end quay

gold added pix