力扣-回溯-37 解数独

思路

双层递归，而且在传递参数使用&的好处是不用在复制一次样本，浪费时间

class Solution {
public:
    bool isVaild(vector<vector<char>> &board, int row, int cal, char val){
        for(int i = 0; i < 9;i++){
            if(board[row][i] == val) return false;
        }
        for(int i = 0; i < 9;i++){
            if(board[i][cal] == val) return false;
        }
        int startRow = (row/3) * 3;
        int startCal = (cal/3) * 3;
        for(int i = startRow; i < startRow+3;i++){
            for(int j = startCal; j < startCal+3; j++ ){
                if(board[i][j] == val) return false;
            }
        }

        return true;
    }

    bool backTracking(vector<vector<char>>& board){
        for(int i = 0; i < board.size(); i++){
            for(int j = 0; j < board[0].size(); j++){
                if(board[i][j] == '.'){
                    for(char k = '1'; k <= '9'; k++){
                        if( isVaild(board, i, j, k)){
                            board[i][j] = k;
                            if(backTracking(board)) return true;
                            board[i][j] = '.';
                        }
                    }
                    return false;
                }
            }
        }
        
        return true;
    }
    void solveSudoku(vector<vector<char>>& board) {
        backTracking(board);
    }
};