<p>There is an <code>m x n</code> rectangular island that borders both the <strong>Pacific Ocean</strong> and <strong>Atlantic Ocean</strong>. The <strong>Pacific Ocean</strong> touches the island&#39;s left and top edges, and the <strong>Atlantic Ocean</strong> touches the island&#39;s right and bottom edges.</p>

<p>The island is partitioned into a grid of square cells. You are given an <code>m x n</code> integer matrix <code>heights</code> where <code>heights[r][c]</code> represents the <strong>height above sea level</strong> of the cell at coordinate <code>(r, c)</code>.</p>

<p>The island receives a lot of rain, and the rain water can flow to neighboring cells directly north, south, east, and west if the neighboring cell&#39;s height is <strong>less than or equal to</strong> the current cell&#39;s height. Water can flow from any cell adjacent to an ocean into the ocean.</p>

<p>Return <em>a <strong>2D list</strong> of grid coordinates </em><code>result</code><em> where </em><code>result[i] = [r<sub>i</sub>, c<sub>i</sub>]</code><em> denotes that rain water can flow from cell </em><code>(r<sub>i</sub>, c<sub>i</sub>)</code><em> to <strong>both</strong> the Pacific and Atlantic oceans</em>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2021/06/08/waterflow-grid.jpg" style="width: 400px; height: 400px;" />
<pre>
<strong>Input:</strong> heights = [[1,2,2,3,5],[3,2,3,4,4],[2,4,5,3,1],[6,7,1,4,5],[5,1,1,2,4]]
<strong>Output:</strong> [[0,4],[1,3],[1,4],[2,2],[3,0],[3,1],[4,0]]
<strong>Explanation:</strong> The following cells can flow to the Pacific and Atlantic oceans, as shown below:
[0,4]: [0,4] -&gt; Pacific Ocean 
&nbsp;      [0,4] -&gt; Atlantic Ocean
[1,3]: [1,3] -&gt; [0,3] -&gt; Pacific Ocean 
&nbsp;      [1,3] -&gt; [1,4] -&gt; Atlantic Ocean
[1,4]: [1,4] -&gt; [1,3] -&gt; [0,3] -&gt; Pacific Ocean 
&nbsp;      [1,4] -&gt; Atlantic Ocean
[2,2]: [2,2] -&gt; [1,2] -&gt; [0,2] -&gt; Pacific Ocean 
&nbsp;      [2,2] -&gt; [2,3] -&gt; [2,4] -&gt; Atlantic Ocean
[3,0]: [3,0] -&gt; Pacific Ocean 
&nbsp;      [3,0] -&gt; [4,0] -&gt; Atlantic Ocean
[3,1]: [3,1] -&gt; [3,0] -&gt; Pacific Ocean 
&nbsp;      [3,1] -&gt; [4,1] -&gt; Atlantic Ocean
[4,0]: [4,0] -&gt; Pacific Ocean 
       [4,0] -&gt; Atlantic Ocean
Note that there are other possible paths for these cells to flow to the Pacific and Atlantic oceans.
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> heights = [[1]]
<strong>Output:</strong> [[0,0]]
<strong>Explanation:</strong> The water can flow from the only cell to the Pacific and Atlantic oceans.
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>m == heights.length</code></li>
	<li><code>n == heights[r].length</code></li>
	<li><code>1 &lt;= m, n &lt;= 200</code></li>
	<li><code>0 &lt;= heights[r][c] &lt;= 10<sup>5</sup></code></li>
</ul>

class Solution {
public:
    int x[4] = {1, -1, 0, 0};
    int y[4] = {0, 0, -1, 1};
    int vis[201][201]={0};
    int dp[201][201]={-1};
    int rec(int i, int j, int n, int m, vector<vector<int>>& heights){
        int ret = 0;
        if(dp[i][j]!=-1){
            return dp[i][j];
        }
        if((i==n-1 && j==0) || (i==0 && j==m-1) ){
            ret =  3;
        } else if(i==0 || j==0){
            ret =  1;
        } if (i==n-1 || j==m-1){
            if(ret == 1 || ret ==3){
                ret=3;
            } else {
                ret =  2;
            }
        }
        int tmp = 0;
        for(int k=0;k<4;k++){
            int ii = i + x[k];
            int jj = j + y[k];
            if(ii >= 0 && ii <= n-1 && jj>=0 && jj<=m-1){
                // cout<<ii<<" "<<jj<<endl;
                if(heights[ii][jj] <= heights[i][j] && vis[ii][jj]==0){
                    vis[ii][jj]=1;
                    tmp = rec(ii, jj, n, m , heights);
                    vis[ii][jj]=0;
                    if(ret==0){
                        ret = tmp;
                    } else if (tmp != 0) {
                        if(tmp == 3){
                            ret = 3;
                        } else if( tmp == 2){
                            if(ret==1){
                                ret=3;
                            }
                        } else if (tmp == 1){
                            if(ret==2){
                                ret=3;
                            }
                        }
                    }
                }
            }
        }
        return dp[i][j]=ret;
    }
    vector<vector<int>> pacificAtlantic(vector<vector<int>>& heights) {
        int n = heights.size();
        int m = 0;
        if(n>0){
            m = heights[0].size();
        }
        vector<vector<int>> ans;
        int tmp;
        memset(dp, -1, sizeof(dp));
        for(int i=0;i<n;i++){
            for(int j=0;j<m;j++){
                memset(vis, 0, sizeof(vis));
                memset(dp, -1, sizeof(dp));
                // cout<<"new"<<endl;
                tmp =rec(i,j,n,m,heights); 
                // cout<<tmp<<endl;
                if(tmp==3){
                      ans.push_back({i,j});
                }
            }
        }
        return ans;
    }
};
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