 Sudoku

A finite constraint satisfaction problem on a $9\times 9$ array. Each entry must be one of the integers $1,\dots ,9$, and every row, column, and designated $3\times 3$ box must contain each value once. Given entries constrain the possible completions; backtracking searches those completions.

Sudoku is a logic-based puzzle that typically consists of a 9x9 grid, which is divided into nine 3x3 subgrids or regions. The objective of the game is to fill the grid in such a way that every row, every column, and every 3x3 subgrid contains all the digits from 1 to 9 without any repetition.