542. 01 Matrix.cpp

class Solution {
public:
    vector<vector<int>> updateMatrix(vector<vector<int>>& matrix)
    {
        int m = matrix.size(), n = matrix[0].size();
        vector<vector<int>> dirs{{0,-1},{-1,0},{0,1},{1,0}};
        queue<pair<int, int>> q;
        for (int i = 0; i < m; ++i)
        {
            for (int j = 0; j < n; ++j)
            {
                if (matrix[i][j] == 0) 
                    q.push({i, j});
                else matrix[i][j] = -1;
            }
        }
        while (!q.empty())
        {
            auto t = q.front(); q.pop();
            for (auto dir : dirs) {
                int x = t.first + dir[0], y = t.second + dir[1];
                if (x < 0 || x >= m || y < 0 || y >= n ||(matrix[x][y] <= matrix[t.first][t.second]&&matrix[x][y]!=-1)) 
                    continue;
                matrix[x][y] = matrix[t.first][t.second] + 1;
                q.push({x, y});
            }
        }
        return matrix;
    }
};