<p>Given an <code>m x n</code> 2D binary grid <code>grid</code> which represents a map of <code>&#39;1&#39;</code>s (land) and <code>&#39;0&#39;</code>s (water), return <em>the number of islands</em>.</p>

<p>An <strong>island</strong> is surrounded by water and is formed by connecting adjacent lands horizontally or vertically. You may assume all four edges of the grid are all surrounded by water.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> grid = [
  [&quot;1&quot;,&quot;1&quot;,&quot;1&quot;,&quot;1&quot;,&quot;0&quot;],
  [&quot;1&quot;,&quot;1&quot;,&quot;0&quot;,&quot;1&quot;,&quot;0&quot;],
  [&quot;1&quot;,&quot;1&quot;,&quot;0&quot;,&quot;0&quot;,&quot;0&quot;],
  [&quot;0&quot;,&quot;0&quot;,&quot;0&quot;,&quot;0&quot;,&quot;0&quot;]
]
<strong>Output:</strong> 1
</pre>

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

<pre>
<strong>Input:</strong> grid = [
  [&quot;1&quot;,&quot;1&quot;,&quot;0&quot;,&quot;0&quot;,&quot;0&quot;],
  [&quot;1&quot;,&quot;1&quot;,&quot;0&quot;,&quot;0&quot;,&quot;0&quot;],
  [&quot;0&quot;,&quot;0&quot;,&quot;1&quot;,&quot;0&quot;,&quot;0&quot;],
  [&quot;0&quot;,&quot;0&quot;,&quot;0&quot;,&quot;1&quot;,&quot;1&quot;]
]
<strong>Output:</strong> 3
</pre>

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

<ul>
	<li><code>m == grid.length</code></li>
	<li><code>n == grid[i].length</code></li>
	<li><code>1 &lt;= m, n &lt;= 300</code></li>
	<li><code>grid[i][j]</code> is <code>&#39;0&#39;</code> or <code>&#39;1&#39;</code>.</li>
</ul>

class Solution {
public:

    void dfs(int i,int j, vector<vector<char>> &grid, map<pair<int,int>,int> &vis, int m,int n)
    {
        
        if(i+1<m && grid[i+1][j]=='1' && vis[{i+1,j}]==0)
        {
            vis[{i+1,j}]=1;
            dfs(i+1,j,grid,vis,m,n);
        }
        if(i-1>=0 && grid[i-1][j]=='1' && vis[{i-1,j}]==0) 
        {
            vis[{i-1,j}]=1;
            dfs(i-1,j,grid,vis,m,n);
        }
        if(j+1<n && grid[i][j+1]=='1' && vis[{i,j+1}]==0) 
        {
            vis[{i,j+1}]=1;
            dfs(i,j+1,grid,vis,m,n);
        }
        if(j-1>=0 && grid[i][j-1]=='1' && vis[{i,j-1}]==0) 
        {
            vis[{i,j-1}]=1;
            dfs(i,j-1,grid,vis,m,n);
        }
        else return;
    }

    int numIslands(vector<vector<char>>& grid) 
    {
        int c=0;
        int m=grid.size();
        int n=grid[0].size();
        map<pair<int,int>,int> vis;
        for(int i=0;i<m;i++)
        {
            for(int j=0;j<n;j++)
            {
                if(grid[i][j]=='1' && vis[{i,j}]==0)
                {
                    vis[{i,j}]=1;
                    c++;
                    dfs(i,j,grid,vis,m,n);
                }
            }
        }
        return c;
    }
};
31595