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The International Obfuscated C Code Contest

2024/burton - Prize in pentagrammatology

wordle hard mode solver

← 2020/yang ↑ 2024 ↑ 2024/cable1 → C code Makefile Inventory Original C ✓

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IOCCC28 - 2024/burton - Prize in pentagrammatology

To build:

 make all

To use:

 ./prog dict

Try:

 ./try.sh

Judges’ remarks:

We were impressed with the algorithm, but one question remains: is there a strategy which reduces the probability of a loss even further, at the cost of requiring a higher average number of guesses?

Author’s remarks:

This program is an assistant for solving hard-mode Wordle(tm) (you must use any revealed hints in all subsequent guesses) accurately/efficiently - in the fewest guesses. The program expects lower case input in two words: guess color, followed by newline.

that correspond to the colors shown in Wordle: g=green, y=yellow, b=black.

Start the program with a single argument, the name of a dictionary of words. /usr/share/dict/words is a perfectly cromulent dictionary, but the included file dict contains the 2315 target words from the original Wordle game and consistently provides the fewest guesses.

As an example session, Wordle 226 has the target word light. The recommended first guess (for all Wordle puzzles) is blast, terns, or crate (see the extra.html that accompanies this entry for details).

Enter terns in game 226 of Wordle, and click the enter button. The letters will turn yellow, black, black, black, black. This assistant prompts "?", and the input expected is the guessed word followed by the first letters of the color revealed for that guess:

 $ ./prog dict
 ? terns ybbbb
 loath
 ? loath gbbyy
 light
 $

The program responds with the recommended next guess. Enter this word loath into the game, which then reveals the colors green, black, black, yellow, yellow. Typing loath gbbyy into this assistant shows the solution is light, and exits. Type this word into the game, click enter, and viola! Solved in 3 guesses: terns > loath > light.

This program averages better than 4 guesses on the 1566 starting words without duplicate letters created by ./dups -n < dict, ranging from 3.587 to 3.997, with an overall average of 3.748 guesses.

This is excellent performance, and close to optimal. See this YouTube presentation on solving Wordle using information theory, which shows a hard mode average of 3.562 when using crane (time offset 29:58). There is a small correction video changing crane to salet, trace or crate. NB: These videos are NOT spoilers for this algorithm.

prog does NOT require you to use its offered guess. If you think you have a better guess than offered, simply type your guess and the Wordle/gen responses into prog; it will internally re-adjust using your input instead of its guess, and produce what it thinks is the best next guess after your input.

A Feature

Caution: When there are duplicate letters in the guess word, and one of them is marked black and the other non-black, this program MUST have the black letter marked yellow. The example session (Wordle 228) below demonstrates this:

 # do NOT do this
 $ ./prog dict
 ? terns bbbby
 shoal
 ? shoal gggbb
 shook
 ? shook gggbg <<-- this is what Wordle shows
 xyzzy <<-- no candidate words match
 # do THIS instead
 $ ./prog dict
 ? terns bbbby
 shoal
 ? shoal gggbb
 shook
 ? shook gggyg <<-- not gggbg as shown in the game
 shock
 ? shock ggggg
 shock

In the guess word shook, there are 2 ‘o’s, but only one shown valid in the puzzle. If you mark the leftmost ’o’ as black (as according to the Wordle game), this program cannot find the winning word (shock), producing the error word xyzzy.

The included simulator gen produces the required transformation of b -> y.

The extra program run connects gen and prog, allowing for quick tests.

 make tools
 ./run dict terns shock # test starting guess `terns` against target `shock`

Using run allows one to quickly and easily experiment with different starting words for different target words, seeing how the guesses progress.

(A late tweak to the program improved its accuracy, and in the above example, the progression is now terns > shoal > shock. However, the caution remains for any duplicate letter guesses.)

Failure mode

The following 4 words from the included file dict are not guessed correctly within 6 guesses when using the recommended (via exhaustive testing) starting guess of blast. Since this program is deterministic, these four words always require 7 guesses when starting with blast, yielding a failure rate of 4/2315, or a success rate of 99.8%.

 foyer jaunt shave wound

Using the ancillary programs run, exhaust, and mkresults, the starting word blast yields the fewest misses at these four words, with an accuracy/efficiency of 3.67. See extra.html for more detail.

This program also has a benefit the game Wordle does not: Wordle allows several thousand extra words to use in guesses not in dict. This program does not restrict any words, so one could enter any combination of 5 letters as input, except these are unlikely to be accepted by the Wordle game, and this program selects its words from the much more limited set that is present in dict. Using an expanded dictionary like /usr/share/dict/words provides a richer set of guesses, but generally increases the average number of guesses and the failure rate.

Interesting questions

Did you notice?

 make spoiler

Time Passages (Apologies to Al Stewart)

This code was written in mid January 2022, before the NYT purchased Wordle[tm].

I have since used this assistant to play the game for more than a year, confirming my local experiments.

wordle stats

The dictionary changed in 2023! In late March 2023, I encountered the first word not in dict: guano. In a bit of a surprise, I tried:

 blast bbgbb
 reach bbgbb
 piano bbggg
 xyzzy

What? The only word in dict ending in ano is piano. So I tried again using /usr/share/dict/words:

 blast bbgbb
 crane bbggb
 guano ggggg

Blending the two, the puzzle was guessed in 4 tries total:

 blast > reach > piano > guano

So caveat emptor: while dict used to be authoritative, we know some words were deemed offensive and removed. More problematic, some words were added, although I am presently unaware of which words. The existence proof is the above mentioned guano. There are almost certainly other words missing.

With guano added to dict, it is guessed in 3 using blast as the starting word:

 blast bbgbb
 reach bbgbb
 guano ggggg

NB: dict has not been changed. gauno was NOT added to dict. Adding this word changes the statistics, and thus requires a change to all this material. It has a slightly negative impact, except for it finds the word guano. Essentially, as you add new words to dict, the permutations expand, and the scores decrease. This is why /usr/share/dict/words scores worse than dict - and loses more often.

April 9, 2023, this problem repeated with the target word snafu. That seems apropos.

 $ ./prog dict
 blast bbgyb
 share gbgbb
 spank gbgyb
 xyzzy
 $ ./prog /usr/share/dict/words
 blast bbgyb
 share gbgbb
 spank gbgyb
 snafu ggggg

And on June 9, 2023, again. This time, it cost nothing, and won on the second guess.

 $ ./prog dict
 blast gyygb
 xyzzy
 $ ./prog /usr/share/dict/words
 blast gyygb
 balsa ggggg

June 19, 2023, another one wasn’t working, so time for a better dictionary:

 $ ./prog dict
 blast bbybb
 ramen bgbbb
 vapid bgbbb
 wacky bgbyb
 xyzzy
 # a copy of /usr/share/dict/words with five letters and no capitals:
 grep '^.....$' /usr/share/dict/words | grep -v '[A-Z]' > ./usdw
 $ ./prog usdw
 blast bbybb
 redan bbbyb
 campo bgbbg
 wahoo bgbgg
 kazoo ggggg

As of June 19, 2023, it is known that at least these words have been added (more are likely). Using ./usdw as above, prog guesses these words in:

 guano 3
 snafu 4
 balsa 2
 kazoo 5

See the extra.html for more details on the program run:

 for n in guano snafu balsa kazoo; do
 ./run usdw blast $n;
 done | grep good

As of April 22, 2024, add the word laser in 3 guesses.

 $ ./prog usdw
 blast byyyb
 solea ybygy
 laser ggggg

And May 8, 2024 brings on pious in 4 guesses (after the failure with dict):

 $ ./prog dict
 blast bbbyb
 siren ygbbb
 ficus bgbgg
 xyzzy
 $ ./prog usdw
 ? blast bbbyb
 serio
 ? siren ygbbb
 pisco
 ? ficus bgbgg
 pious
 ? pious ggggg

Notice here that the suggested word was NOT used, instead the original guesses were used, and it found the correct answer in 4 guesses. However, doing

 ./run usdw blast pious

gets the answer correct in 3 guesses: blast > serio > pious.

And Sep 17, 2024 brings us the word beaut.

 $ ./prog dict
 blast gbgbg
 xyzzy
 $ ./prog usdw
 blast gbgbgb
 beant -- not allowed, so removed beant from usdw
 brant gbgbg
 beaut ggggg

Three guesses using an alternate dictionary and having to remove beant. This word isn’t even a word I can find in Webster’s. I hope your version of /usr/share/dict/words has more cromulent words.

Oct 9, 2024 brings the word mommy.

 $ ./prog dict
 blast bbbbb
 drone bbybb
 pouch bgbbb
 foggy bgbbg
 $ ./prog usdw
 blast bbbbb
 drone bbybb
 pouch bgbbb
 foggy bgbbg
 mommy ggggg

Fortunately, the program is good enough that failing with one dictionary still allows you to switch dictionaries and win.

Nov 13, 2024 brings primp.

 $ ./prog dict
 blast bbbbb
 drone bgbbb
 crimp bgggg
 xyzzy
 $ ./prog usdw
 blast bbbbb
 drone bgbbb
 crimp bgggg
 primp ggggg

Jan 20, 2025 brings the word squid.

 $ ./prog dict
 blast bbbyb
 siren gybbb
 skimp gbybb
 sushi <<-- last plausible word
 $ ./prog usdw
 blast bbbyb
 siren gybbb
 skimp gbybb
 sushi sgbby
 squid ggggg

As of Jan 20, 2025, the ten known words not in dict are (scores are using usdw, not dict, which lacks these words):

 guano 4
 snafu 5
 balsa 3
 kazoo 4
 laser 3
 pious 4
 beaut 3
 mommy 4
 primp 5
 squid 4

Feb 18, 2025 adds a word not in dict nor usdw. "indie".

 $ ./prog dict
 blast bbbbb
 drone ybbyg
 undue bggbg
 xyzzy
 $ ./prog usdw
 blast bbbbb
 drone ybbyg
 undue bggbg
 xyzzy

I grep’d the dictionaries. No plausbile hits. So I solved it the old fashioned way: I guessed.

blast bbbbb drone ybbyg undue bggbg indie ggggg

This solved it in 4, but the program could not win. So add to the summary list above:

indie 4

Compilation

Compiles cleanly with -Wall -Wpedantic -Wextra, on MACOS M2 Clang/GCC 14 and Linux X86 Gcc 8.5.

If you are using -Weverything, which IMHO is exceptionally noisy about non-problems, and given the requirements of obfuscation and layout, there are a few -Wno- flags required to achieve a quiet compilation:

 -Wno-poison-system-directories \
 -Wno-missing-variable-declarations \
 -Wno-shadow \
 -Wno-vla \
 -Wno-missing-prototypes \
 -Wno-shorten-64-to-32 \
 -Wno-format-nonliteral \
 -Wno-implicit-int-conversion \
 -Wno-declaration-after-statement \
 -Wno-comma \
 -Wno-array-bounds-pointer-arithmetic \
 -Wno-sign-conversion

The code uses variable length arrays, omitted the keyword static for functions and global variables, and collide size_t with int for return types. There are no pedantic prototypes for functions. There is no misuse of the comma operator, but try getting the compiler to ignore it. The code has been run on MacOS M2 and Linux x86 with no failures observed. And as documented in deobfuscated.html, pointer bounds are intentionally abused for obfuscation, but the code is correct as documented. This is obfuscated C, so yes, variables are intentionally shadowed. printf() is also abused, passing in non-literals as the format.

Perhaps there is some platform out there that won’t work correctly due to the omissions noted above, but I am unaware of these.

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