286.墙与门 (Medium)*

class Solution {
public:
    void wallsAndGates(vector<vector<int>>& rooms) {
        int m = rooms.size();
        if(m == 0) {
            return;
        }
        int n = rooms[0].size();
        if(n == 0) {
            return;
        }
        queue<pair<int, int>> q;
        for(int i = 0; i < m; i++) {
            for(int j = 0; j < n; j++) {
                if(rooms[i][j] == 0) {
                    q.push(make_pair(i, j));
                }
            }
        }
        vector<pair<int, int>> dirs = {{-1, 0}, {1, 0}, {0, -1}, {0, 1}};
        int depth = 0;
        while(!q.empty()) {
            // int len = q.size();
            // while(len--) {
                int x = q.front().first;
                int y = q.front().second;
                q.pop();
                for(auto d : dirs) {
                    int nextX = d.first + x;
                    int nextY = d.second + y;
                    if(nextX < 0 || nextY < 0 || nextX >= m || nextY >= n || rooms[nextX][nextY] == -1) {
                        continue;
                    }
                    if(rooms[nextX][nextY] > rooms[x][y] + 1) {
                        rooms[nextX][nextY] = rooms[x][y] + 1;
                        q.push(make_pair(nextX, nextY));
                    }

                }
            // }
        }
    }
};