<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, vector<vector<int>>& visited, int row, int col ){
        if(i >= row || j >= col || i < 0 || j < 0) return;
        if(grid[i][j] != '1' || visited[i][j] == 1) return;
            visited[i][j] = 1;
            dfs(i-1, j, grid, visited, row, col);
            dfs(i+1, j, grid, visited, row, col);
            dfs(i, j-1, grid, visited, row, col);
            dfs(i, j+1, grid, visited, row, col);
    }
    int numIslands(vector<vector<char>>& grid) {
        int row = grid.size();
        int col = grid[0].size();
        int count = 0;
        vector<vector<int>> visited(row);
        for(int i=0; i<row; i++){
            for(int j=0; j<col; j++){
                 visited[i].push_back(0);
             }
         }

        for(int i=0; i<row; i++){
            for(int j=0; j<col; j++){
               if(visited[i][j] == 0 && grid[i][j] == '1'){
                    count++;
                    dfs(i, j, grid, visited, row, col);
                }
            }
        }
       return count;
    }
};
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