LeetCode OJ：Sudoku Solver（数独游戏）

Write a program to solve a Sudoku puzzle by filling the empty cells.

Empty cells are indicated by the character '.'.

You may assume that there will be only one unique solution.

A sudoku puzzle...

...and its solution numbers marked in red.

dfs,一直寻找，不行返回即可：

class Solution {
public:
    void solveSudoku(vector<vector<char>>& board) {
        doSudoku(board);
    }

    bool checkValid(vector<vector<char>>&board, int x, int y)
    {
        for(int i = 0; i < 9; i++){
            if(i!=x)
                if(board[i][y] == board[x][y]) return false;
        }

        for(int j = 0; j < 9; j++){
            if(j != y)
                if(board[x][j] == board[x][y]) return false;
        }

        for(int i = (x/3) * 3; i < (x/3 + 1) * 3; ++i){
            for(int j = (y/3) * 3; j < (y/3 + 1) * 3; ++j){
                if((i!=x) || (j != y))
                    if(board[x][y] == board[i][j]) return false;
            }
        }
        return true;
    }

    bool doSudoku(vector<vector<char>> & board)
    {
        for(int row = 0; row < 9; ++row){
            for(int col = 0; col < 9; ++col){
                if(board[row][col] == '.'){
                    for(int i = 1; i <= 9; ++i){
                        board[row][col] = '0' + i;
                        if(checkValid(board, row, col)){
                            if(doSudoku(board)){
                                return true;
                            }
                        }    
                        board[row][col] = '.';
                    }
                    return false;
                }
            }
        }
        return true;
    }
};