<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:
    bool isvalid( int row, int col,vector<vector<int>>& grid){
        if(row<0||row>=grid.size()) return false;
        if(col<0||col>=grid[0].size()) return false;
        return true;
    }
    
   int dr[4]={-1,0,1,0};
    int dc[4]={0,1,0,-1};
   void bfs(vector<vector<int>>& heights,vector<vector<int>> &ocean,vector<vector<bool>>&visit){
    queue<pair<int,int>> q;
 
    for(vector<int> m:ocean){
        q.push({m[0],m[1]});
        visit[m[0]][m[1]]=true;
           
    }

     while(!q.empty()){
        pair<int,int> cur=q.front();
       
        q.pop(); 
        for(int i=0;i<4;i++){
           if(isvalid(cur.first+dr[i],cur.second+dc[i],heights)&&!visit[cur.first+dr[i]][cur.second+dc[i]]&&heights[cur.first+dr[i]][cur.second+dc[i]]>=heights[cur.first][cur.second]){
               q.push({cur.first+dr[i],cur.second+dc[i]});
                visit[cur.first+dr[i]][cur.second+dc[i]]=true;
                
            }
        }
     }
   }
    
    vector<vector<int>> pacificAtlantic(vector<vector<int>>& heights) {
        vector<vector<int>> pacific;
         vector<vector<bool>> reach_pacific(heights.size(),vector<bool>(heights[0].size()));
         vector<vector<int>> atlantic;
         vector<vector<bool>> reach_atlantic(heights.size(),vector<bool>(heights[0].size())); 
        vector<vector<int>> res;
        vector<vector<bool>> visit(heights.size(),vector<bool>(heights[0].size()));
        for(int i=0;i<heights.size();i++){
            pacific.push_back({i,0});
            int n=heights[0].size()-1;
             atlantic.push_back({i,n});

        }  
           for(int i=0;i<heights[0].size();i++){
            pacific.push_back({0,i});
            int n=heights.size()-1;
             atlantic.push_back({n,i});

        }  
        bfs(heights,pacific,reach_pacific);
        bfs(heights,atlantic,reach_atlantic);
         for(int i=0;i<heights.size();i++){
           for(int j=0;j<heights[0].size();j++){
             if(reach_atlantic[i][j]&&reach_pacific[i][j])
             res.push_back({i,j});
        }  
         }
         return res;

      
        
        
    }
};
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