<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 {
private:
    void dfs(int r, int c, vector<vector<int>>& vis, vector<vector<char>>& grid, int drow[], int dcol[]){
        vis[r][c] = 1;
        int n = grid.size();
        int m = grid[0].size();
        //Traverse
        for(int i = 0; i < 4; i++){
            int nr = r + drow[i];
            int nc = c + dcol[i];

            if(nr >= 0 && nr < n && nc >= 0 && nc < m && 
            !vis[nr][nc] && grid[nr][nc] == '1')
                dfs(nr, nc, vis, grid, drow, dcol);
        }
    }
public:
    int numIslands(vector<vector<char>>& grid) {
        int n = grid.size();
        int m = grid[0].size();

        int drow[] = {0, 0, -1, +1};
        int dcol[] = {-1, +1, 0, 0};

        vector<vector<int>> vis(n, vector<int> (m, 0));
        int cnt = 0;
        for(int i = 0; i < n; i++){
            for(int j = 0; j < m; j++){
                if(!vis[i][j] && grid[i][j] == '1'){
                    cnt++;
                    dfs(i, j, vis, grid, drow, dcol);
                }
            }
        }

        return cnt;
    }
};
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