Судоку

The playing field is a square 9 × 9, divided into smaller squares with sides of 3 cells. Thus, all the playing field consists of 81 cells. They are already in the beginning of the game are some numbers (1 to 9), called the tips. The player is required to fill the empty cells with numbers from 1 to 9 so that in each row, each column and each small square 3 × 3 each digit met only once. The application has three modes: Easy, Normal and Difficult levels. In a light level in each line are already numbers 7-6, 5-4 on the average level, and complicated figures 3-2 respectively.