<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:

    vector<vector<bool>> visited;
    vector<vector<bool>> grd;

    int dr[4] = {-1,0,0,1};
    int dc[4] = {0,1,-1,0};

    void dfs(int r, int c)
    {
        if(visited[r][c]) return;
        visited[r][c] = true;

        for(int i = 0; i < 4; i++)
        {
            int nr = r + dr[i];
            int nc = c + dc[i];
            if(nr >= 0 && nc >= 0 && nr < grd.size() && nc < grd[0].size() && grd[nr][nc]) dfs(nr,nc);
        }
    }

    int numIslands(vector<vector<char>>& grid) {
        for(int i = 0; i < grid.size(); i++)
        {
            visited.push_back(vector<bool>());
            grd.push_back(vector<bool>());
            for(int j = 0; j < grid[i].size(); j++)
            {
                visited[i].push_back(false);
                grd[i].push_back(grid[i][j] == '1');
            }
        }

        int res=0;

        for(int i = 0; i < grid.size(); i++)
        {
            for(int j = 0; j < grid[i].size(); j++)
            {
                if(grd[i][j] && !visited[i][j])
                {
                    dfs(i,j);
                    res++;
                }
            }
        }

        return res;
    }
};
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