<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 {
    vector<vector<int>>a;
    int n,m;
public:
    vector<vector<int>> shared_n(vector<int>& x,vector<int>& y){
        vector<vector<int>>ans(n,vector<int>(m,0));
        for(int i=0;i<x.size();i++){
            ans[y[i]][x[i]]=1;
        }
        for(int i=0;i<x.size();i++){
            // cout<<x[i]<<" "<<y[i]<<endl;
            if(x[i]<m-1){
                if(ans[y[i]][x[i]+1]==0 && a[y[i]][x[i]]<=a[y[i]][x[i]+1]){
                    ans[y[i]][x[i]+1]=1;
                    x.push_back(x[i]+1);
                    y.push_back(y[i]);
                }
            }
            if(x[i]>0){
                if(ans[y[i]][x[i]-1]==0 && a[y[i]][x[i]]<=a[y[i]][x[i]-1]){
                    ans[y[i]][x[i]-1]=1;
                    x.push_back(x[i]-1);
                    y.push_back(y[i]);
                }
            }
            if(y[i]<n-1){
                if(ans[y[i]+1][x[i]]==0 && a[y[i]][x[i]]<=a[y[i]+1][x[i]]){
                    ans[y[i]+1][x[i]]=1;
                    x.push_back(x[i]);
                    y.push_back(y[i]+1);
                }
            }
            if(y[i]>0){
                if(ans[y[i]-1][x[i]]==0 && a[y[i]][x[i]]<=a[y[i]-1][x[i]]){
                    ans[y[i]-1][x[i]]=1;
                    x.push_back(x[i]);
                    y.push_back(y[i]-1);
                }
            }
        }
        return ans;
    }

    vector<vector<int>>pacific(){
        vector<int>x,y;
        int i;
        for(i=0;i<n;i++){
            x.push_back(0);
            y.push_back(i);
        }
        for(i=0;i<m;i++){
            x.push_back(i);
            y.push_back(0);;
        }
        return shared_n(x,y);
    }
    vector<vector<int>>atlantic(){
        vector<int>x,y;
        int i;
        for(i=0;i<n;i++){
            x.push_back(m-1);
            y.push_back(i);
        }
        for(i=0;i<m;i++){
            x.push_back(i);
            y.push_back(n-1);;
        }
        return shared_n(x,y);
    }
    vector<vector<int>> pacificAtlantic(vector<vector<int>>& heights) {
        a=heights;
        n=a.size(),m=a[0].size();
        vector<vector<int>>val1=pacific();
        vector<vector<int>>val2=atlantic();
        vector<vector<int>>ans;
        vector<int>v(2);
        for(int i=0;i<n;i++){
            for(int j=0;j<m;j++){
                // cout<<val1[i][j]<<val2[i][j]<<" ";
                if(val1[i][j]&&val2[i][j]){
                    v[0]=i;
                    v[1]=j;
                    ans.push_back(v);
                }
            }
            // cout<<endl;
        }
        return ans;
    }
};
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