数独问题

本题源自leetcode   37

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思路： 1 用回溯法。从（0,0)开始访问数组，试着将1-9填充。

代码：

  void solveSudoku(vector<vector<char>>& board) {
        int row = board.size();
        if(row != 9)
            return ;
        int col = board[0].size();
        if(col != 9)
            return;
        solveSudo(board,0,0);
    }
    bool solveSudo(vector<vector<char>>& board,int i,int j){
        if(i == 9)
            return true;
        if(j == 9)
            return solveSudo(board,i + 1, 0);
        if(board[i][j] != '.') //说明已经填数了，直接进入下一个位置
            return solveSudo(board,i, j + 1);
        for(char c = '1'; c <= '9'; c++){
            if(check(board,i, j, c)){  //回溯法
                board[i][j] = c;
                if(solveSudo(board, i, j + 1))  
                    return true;
                board[i][j] = '.';
            }
        }
        return false;
    }
    bool check(vector<vector<char>>& board,int i, int j, char val){
        int row = i - i%3, col = j - j%3;
        for(int m = 0; m < 9; m++){  //检查每一列
            if(board[m][j] == val)
                return false;
        }
        for(int m = 0; m< 9; m++){  //检查每一行
            if(board[i][m] == val)
                return false;
        }
        for(int m = 0; m < 3; m++){  //检查每一个框
            for(int n = 0; n < 3; n++){
                if(board[m+row][n+col] == val)
                    return false;
            }
        }
        return true;
    }