I am working on an optimized Sudoku solver. The basic idea of backtracking remains, though I have added forward checking. The domain (what numbers can be set into a cell) is stored for every cell. Before I try to set a number into a cell and backtrack if it doesn’t work, I check all the related cells to see if the number is the only one that could be set there. If a conflict occurs, I try the next number, and so on. Optimally, this reduces the amount of backtracking necessary.