<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 isIsland(vector<vector<char>>& grid,int x,int y,vector<vector<int>>& visited){
        if(!visited[x][y]){
            visited[x][y] = 1;
            int dx[4] = {+1,-1,0,0};
            int dy[4] = {0,0,-1,+1};

            for(int i=0; i<4; i++){
                int row = x + dx[i];
                int col = y + dy[i];
                if(row < grid.size() && row >=0 && col < grid[0].size() && col>=0 && grid[row][col] == '1'){
                    isIsland(grid,row,col,visited);
                }
            }

            
        }
    }

    int numIslands(vector<vector<char>>& grid) {
        ios_base::sync_with_stdio(false);
        cout.tie(NULL);
        cin.tie(NULL);

        int n = grid.size();
        int m = grid[0].size();
        vector<vector<int>> visited(n,vector<int>(m,0));
        
        int cnt = 0;

        for(int i=0; i < n; i++){
            for(int j =0; j < m; j++){
                if(grid[i][j] == '1' && !visited[i][j]){
                    isIsland(grid,i,j,visited);
                    cnt++;
                }
            }
        }

        return cnt;
    }
};
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