This project is done in C for the course of OS, in which pthreads are used to validate the solution of the puzzle. Moreover the game has 3 difficulty levels based upon the number of empty spaces on board. In the validator, total 11 threads are created. 1 for rows, 1 for columns and 9 for 9 grids of 3x3 cells. The major focus was on use of threads for building sudoku validator and then game was added to it afterwards.