LeetCode: Sudoku Solver

看了网上答案，发现一个很有趣的问题，check函数里形参board是传值时（即&board)速度很快，能过large，去掉这个&后就过不了large了，是不是因为没有传值的话每次需要复制这样耗了时间了呢

class Solution {
public:
    bool check(int x, int y, vector<vector<char>> &board) {
        bool flag[9] = {false};
        for (int i = 0; i < 9; i++) 
            if (board[x][i] != '.') 
                if (!flag[board[x][i]-'1']) flag[board[x][i]-'1'] = true;
                else return false;
        memset(flag, false, 9);
        for (int i = 0; i < 9; i++) 
            if (board[i][y] != '.')
                if (!flag[board[i][y]-'1']) flag[board[i][y]-'1'] = true;
                else return false;
        memset(flag, false, 9);
        int xx = x/3*3;
        int yy = y/3*3;
        for (int i = 0; i < 3; i++)
            for (int j = 0; j < 3; j++) 
                if (board[xx+i][yy+j] != '.')
                    if (!flag[board[xx+i][yy+j]-'1']) flag[board[xx+i][yy+j]-'1'] = true;
                    else return false;
        return true;
    }
    bool dfs(vector<vector<char>> &board) {
        for (int i = 0; i < 9; i++) {
            for (int j = 0; j < 9; j++) {
                if (board[i][j] == '.') {
                    for (char k = '1'; k <= '9'; k++) {
                        board[i][j] = k;
                        if (check(i, j, board) && dfs(board)) return true;
                        board[i][j] = '.';
                    }
                    return false;
                }
            }
        }
        return true;
    }
    void solveSudoku(vector<vector<char> > &board) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        dfs(board);
    }
};

 C#

public class Solution {
    public void SolveSudoku(char[,] board) {
        dfs(board);
        
    }
    public bool dfs(char[,] board) {
        for (int i = 0; i < 9; i++) {
            for (int j = 0; j < 9; j++) {
                if (board[i, j] == '.') {
                    for (char k = '1'; k <= '9'; k++) {
                        board[i, j] = k;
                        if (check(i, j, board) && dfs(board)) return true;
                        board[i, j] = '.';
                    }
                    return false;
                }
            }
        }
        return true;
    }
    public bool check(int x, int y, char[,] board) {
        bool[] flag = new bool[9];
        for (int i = 0; i < 9; i++) {
            if (board[x, i] != '.') {
                if (!flag[board[x, i] - '1']) flag[board[x, i] - '1'] = true;
                else return false;
            }
        }
        flag = new bool[9];
        for (int i = 0; i < 9; i++) 
            if (board[i, y] != '.')
                if (!flag[board[i, y]-'1']) flag[board[i, y]-'1'] = true;
                else return false;
        flag = new bool[9];
        int xx = x/3*3;
        int yy = y/3*3;
        for (int i = 0; i < 3; i++)
            for (int j = 0; j < 3; j++) 
                if (board[xx+i, yy+j] != '.')
                    if (!flag[board[xx+i, yy+j]-'1']) flag[board[xx+i, yy+j]-'1'] = true;
                    else return false;
        return true;
    }
}