mastermind-solver

A parallel C program that plays Mastermind for you.

This is not a full implementation of the board game Mastermind; it's an engine that helps you win it in as few guesses as possible.

The computations are parallelized with OpenMP. You can choose between two strategies: optimize the average case or the worst case.

Settings

Before compilation, adjust three constants at the top of the source file:

• NUM_COLORS: number of available colors (default: 6)
• CODE_LENGTH: length of the secret code (default: 4)
• WORST_CASE: optimize worst case if true, average case if false

Compilation

After changing the constants, compile with:

gcc -O3 -fopenmp mastermind-solver.c -o mastermind

Running the solver

Example run with CODE_LENGTH=4, NUM_COLORS=6, and WORST_CASE=false:

./mastermind yellow red blue green pink white

If the secret code were [green yellow yellow pink], the interaction could look like this:

SETTINGS:

Code length: 4
Number of colors: 6
Maximum number of guesses: 12
Mode: average case
Colors: yellow red blue green pink white

********************************************************************************

There are still 1296 valid combinations.
The expected number of valid combinations after the next reply is 185.27.

My proposed combination for guess 1 is:

   white     pink   yellow    white 

My proposed guess is valid and could be the solution.

Please enter the number of black pins: 1
Please enter the number of white pins: 1

********************************************************************************

There are still 230 valid combinations.
The expected number of valid combinations after the next reply is 27.20.

My proposed combination for guess 2 is:

    blue    white    green    white 

My proposed guess is valid and could be the solution.

Please enter the number of black pins: 0
Please enter the number of white pins: 1

********************************************************************************

There are still 41 valid combinations.
The expected number of valid combinations after the next reply is 4.05.

My proposed combination for guess 3 is:

    pink   yellow   yellow     blue 

My proposed guess is valid and could be the solution.

Please enter the number of black pins: 2
Please enter the number of white pins: 1

********************************************************************************

There are still 4 valid combinations.
The expected number of valid combinations after the next reply is 0.75.

My proposed combination for guess 4 is:

   green   yellow   yellow     pink 

My proposed guess is valid and could be the solution.

Please enter the number of black pins: 4
Please enter the number of white pins: 0

Done! Solved in 4 guesses!

What the code does

The solver is randomized and will usually give different suggestions even with the same input.

To propose the next guess, it evaluates all possible guesses and assigns a score. It assumes every currently feasible secret code is equally likely, which gives probabilities for each reply (counts of black and white pins). Using this, the solver minimizes the number of potential solutions after the next reply: with WORST_CASE=false, it minimizes the expected number; with WORST_CASE=true, it minimizes the maximum number across all replies.