Sudoku, sometimes spelled Su Doku (sudoko, sodoku), is a placement puzzle, also known as Number Place in the United States.
    * Enter digits from 1 to 9 into the blank spaces.
    * Every row must contain one of each digit. So must every column, as must every 3x3 square.
    * It has a unique solution that can be reached logically without guessing.
    * It's fun. It's challenging. It's addictive!