Sudoku Solver

You are given a partially filled Sudoku grid. Your task is to fill the grid completely following the Sudoku rules. Print the completed grid, or print 'NO SOLUTION' if it cannot be solved. Input Format: The first line contains an integer N (1 <= N <= 9). The next N lines contain N integers (0 for empty cells). Output Format: Print the completed grid or 'NO SOLUTION' if it is impossible. Example Input: 9 5 3 0 0 7 0 0 0 0 6 0 0 1 9 5 0 0 0 0 9 8 0 0 0 0 6 0 8 0 0 0 6 0 0 0 3 4 0 0 8 0 3 0 0 1 7 0 0 0 2 0 0 0 6 0 6 0 0 0 0 2 8 0 0 0 0 4 1 9 0 0 5 0 0 0 0 8 0 0 7 9 Example Output: 5 3 4 6 7 8 9 1 2 6 7 2 1 9 5 3 4 8 1 9 8 3 4 2 5 6 7 8 5 9 7 6 1 4 2 3 4 2 6 8 5 3 7 9 1 7 1 3 9 2 4 8 5 6 9 6 1 2 3 5 7 8 4 2 8 7 4 1 9 6 3 5 3 4 5 8 8 6 1 7 9