<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 visit(vector<vector<char>>& grid,vector<vector<bool>>& visited,int m,int n, int row, int col){
        queue<pair<int,int>> q;
        q.push(make_pair(m,n));
        visited[m][n]=true;
        vector<vector<int>> dir={{-1,0},{1,0},{0,-1},{0,1}};
        while(!q.empty()){
            int r=q.front().first;
            int c=q.front().second;
            q.pop();
            for(int i=0;i<4;i++){
                if(r+dir[i][0]>=0 && r+dir[i][0]<row && c+dir[i][1]>=0 && c+dir[i][1]<col && !visited[r+dir[i][0]][c+dir[i][1]] && grid[r+dir[i][0]][c+dir[i][1]]=='1'){
                    q.push(make_pair(r+dir[i][0],c+dir[i][1]));
                    visited[r+dir[i][0]][c+dir[i][1]]=true;
                }
            }
        }
    }
    int numIslands(vector<vector<char>>& grid) {
        int m=grid.size();
        int n=grid[0].size();
        vector<vector<bool>> visited(m,vector<bool>(n,false));
        int sum=0;
        for(int i=0;i<m;i++){
            for(int j=0;j<n;j++){
                if(grid[i][j]=='1' && visited[i][j]==false){
                    visit(grid,visited,i,j,m,n);
                    sum++;
                }
            }
        }
        return sum;
    }
};
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