LeetCode37. Sudoku Solver

1. Topic Link

   Portal

2. The meaning of problems

   Sudoku games we have played, this question is given a 9 x 9 Sudoku board, you need to give a final legal chessboard

3. Problem-solving ideas

   Like, see the code search mode at each position searches dfs feasible solution, not burst dfs layer stack 81, at ease dfs

4. AC Code

    class Solution {
   
        public void solveSudoku(char[][] board) {
            solve(board, 0);
        }
   
        public boolean solve(char[][] board, int num) {
            if(num == 81) return true;
   
            int row = num / 9, col = num % 9;
            if(board[row][col] == '.') {
                for(char ch = '1'; ch <= '9'; ++ch) {
                    if(isVaild(board, row, col, ch)) {
                        board[row][col] = ch;
                        if(solve(board, num + 1))
                            return true;
                        else
                            board[row][col] = '.';
                    }
                }
                return false;
            }
            return (solve(board, num + 1));
        }
   
        public boolean isVaild(char[][] board, int r, int c, char ch) {
            for(int i = 0; i < 9; i++) {
                if(board[i][c] == ch) return false;
                if(board[r][i] == ch) return false;
                if(board[3 * (r / 3) + i / 3][3 * (c / 3) + i % 3] == ch) return false;
            }
            return true;
        }
    }

5. PS

   The first time you use the markdown blog, rusty and stiff, 555 ~