## Simple Singles

The first and easiest strategy to attack is certainly Simple Singles. This strategy relies on the basic rule of Sudoku, which states that each row, column, or block must contain the complete set of integers one through nine. This means that if a row, column, or block already has eight of nine cells filled with a value, it follows that the unfilled cell must contain whatever value the other eight cells do not. For example, in Figure 1, the bottom right cell must contain nine because it is the last remaining unused value in the block. Programming this strategy is straightforward. One can go through each empty cell, and if by looking at the row, column, or block it is the only empty cell, then assign it the remaining value.