417.pacific-atlantic-water-flow.cpp

class Solution {
public:
    int max_row, max_col;
    vector<vector<int>> pacificAtlantic(vector<vector<int>>& matrix) {
vector<vector<int>> r;
        int m = matrix.size();
        if (m == 0)
            return r;
        int n = matrix[0].size();
        if (n == 0)
            return r;
        vector<vector<bool>> pacific(m, vector<bool>(n));
        vector<vector<bool>> atlantic(m, vector<bool>(n));
        
        for (int i = 0; i < m; i++) {
            dfs(matrix, pacific, i, 0);
            dfs(matrix, atlantic, i, n-1);

        }
        for (int j = 0; j < n; j++) {
            dfs(matrix, pacific, 0, j);
            dfs(matrix, atlantic, m-1, j);
        }

        
        for (int i = 0; i < m; i++) {
            for (int j = 0; j < n; j++) {
                if (pacific[i][j] && atlantic[i][j])
                    r.push_back({i,j});
            }
        }
        return r;
    }
    
    void dfs(vector<vector<int>>& matrix, vector<vector<bool>>& visited, int i, int j) {
        int m = matrix.size();
        int n = matrix[0].size();

        visited[i][j] = true;
        //up
        if (i-1 >= 0 && visited[i-1][j] != true && matrix[i-1][j]>=matrix[i][j])
            dfs(matrix, visited, i-1, j);
        //down
        if (i+1 < m && visited[i+1][j] != true && matrix[i+1][j]>=matrix[i][j])
            dfs(matrix, visited, i+1, j);
        //left
        if (j-1 >= 0 && visited[i][j-1] != true && matrix[i][j-1]>=matrix[i][j])
            dfs(matrix, visited, i, j-1);
        //right
        if (j+1 <n && visited[i][j+1] != true && matrix[i][j+1]>=matrix[i][j])
            dfs(matrix, visited, i, j+1);

    }
};