<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:
    int numIslands(vector<vector<char>>& grid) {
        int n=grid.size(),m=grid[0].size(),cnt=0,i,j;
        vector<vector<int>>vis(n,vector<int>(m,0));
        for(i=0;i<n;i++)
        {
            for(j=0;j<m;j++)
            {
                if(grid[i][j]=='1' && !vis[i][j])
                {
                    cnt++;
                    bfs(i,j,vis,grid,n,m);
                }
            }
        }
        return cnt;
    }
    void bfs(int row,int col,vector<vector<int>>&vis,vector<vector<char>>&grid,int n,int m)
    {
        queue<pair<int,int>>q;
        vis[row][col]=1;
        q.push({row,col});
        vector<pair<int, int>> directions = {{-1, 0}, {1, 0}, {0, -1}, {0, 1}};
        while(!q.empty())
        {
            int row=q.front().first,col=q.front().second;q.pop();
            for(auto it:directions)
            {
                int nrow=row+it.first,ncol=col+it.second;
                if(nrow>=0&&ncol>=0&&nrow<n&&ncol<m&&grid[nrow][ncol]=='1'&&!vis[nrow][ncol])
                {
                    q.push({nrow,ncol});
                    vis[nrow][ncol]=1;
                }

            }
        }
    }
};
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