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417. Pacific Atlantic Water Flow.cpp
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417. Pacific Atlantic Water Flow.cpp
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class Solution {
public:
void dfs(vector<vector<int>>& h, vector<vector<bool>>& vis, int i, int j) {
int m = h.size();
int n = h[0].size();
vis[i][j] = true;
//up
if (i-1 >= 0 && vis[i-1][j] != true && h[i-1][j] >= h[i][j])
dfs(h, vis, i-1, j);
//down
if (i+1 < m && vis[i+1][j] != true && h[i+1][j] >= h[i][j])
dfs(h, vis, i+1, j);
//left
if (j-1 >= 0 && vis[i][j-1] != true && h[i][j-1] >= h[i][j])
dfs(h, vis, i, j-1);
//right
if (j+1 < n && vis[i][j+1] != true && h[i][j+1] >= h[i][j])
dfs(h, vis, i, j+1);
}
vector<vector<int>> pacificAtlantic(vector<vector<int>>& heights) {
vector<vector<int>>ans;
int m = heights.size();
int n = heights[0].size();
vector<vector<bool>> pacific(m, vector<bool>(n));
vector<vector<bool>> atlantic(m, vector<bool>(n));
for (int i = 0; i < m; i++) {
dfs(heights, pacific, i, 0);
dfs(heights, atlantic, i, n-1);
}
for (int j = 0; j < n; j++) {
dfs(heights, pacific, 0, j);
dfs(heights, 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]) ans.push_back({i,j});
}
}
return ans;
}
};