Word Guess

When you submit a guess, coloring the boxes Green (correct letter, correct spot), Yellow (correct letter, wrong spot), or Gray (wrong letter) seems simple. But a naive implementation will have severe bugs when it comes to duplicate letters.

Imagine the secret word is APPLE and you guess PAPER.

A naive algorithm loops through your guess one letter at a time:

1. Is P in APPLE? Yes! Color it Yellow.
2. Is A in APPLE? Yes! But not in this spot. Color it Yellow.
3. Is P in APPLE? Yes, in this exact spot! Color it Green.

Wait, the secret word only has two P's, but the algorithm just colored both of your P's (one Yellow, one Green), and might even color a third if you guessed PPPPP. This gives the player incorrect information about the word's letter counts.

To fix this, the game uses a Two-Pass Evaluation Algorithm:

• Pass 1 (Find Exacts): Find all the exact matches (Greens) first. When a Green is found, cross that letter out of a temporary copy of the secret word so it can't be matched again.
• Pass 2 (Find Partials): Look at the remaining letters in your guess. If the letter exists in the remaining letters of the temporary secret word, color it Yellow and cross it out. Otherwise, color it Gray.