Mastermind Solver

1. Uses six letters instead of six colors.
2. Input a puzzle (e.g. "bfab") and press <Enter>.
3. The solver starts by picking a random letter and its succeeding neighbor. Each letter is guessed twice.
4. After the answer is computed, pressing <Enter> again will solve the same puzzle again. If a different random letter is chosen, the answer will take a different path.

1. If "black + white = 0", then each letter in the guess should be eliminated from every slot.
2. If "black = 0", then each letter in the guess should be removed from the position it holds in the guess.
3. If "black + white = 4", then start guessing permutations of the current guess.
4. A potential guess is invalid if it contradicts feedback from any previous guesses.

1. GuessOne - pick a randow letter and its succeeding neighbor
2. GuessTwo - pick the next two neighbors
3. GuessCompute - cycle through all remaining combinations (like an odometer), applying rule 4 before submitting each guess
4. GuessPermute - cycle through all permutations, applying rule 4 before submitting each guess