<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 {
    
    int X, Y;
    int islands = 0;
    const int dx[4] = {-1, 1, 0, 0};
    const int dy[4] = {0, 0,-1, 1};
    int visited[301][301] = {0};
    void search(int y, int x, vector<vector<char>> &m)
    {
        if (y < 0 || x < 0 || y >= Y || x >= X)
        {
            return;
        }
        
        if (visited[y][x] == 0 && m[y][x] == '1')
        {
            visited[y][x] = 1;
            for(int i = 0; i < 4; i++)
            {
                if ((y+dy[i]) >= 0 && (x+dx[i]) >= 0 && (y+dy[i]) < Y && (x+dx[i]) < X && m[y+dy[i]][x+dx[i]] == '1')
                {
                    search(y+dy[i], x+dx[i], m);
                }
                
            }
            
            
        }
    }
public:
    int numIslands(vector<vector<char>>& grid) {
        
        Y = grid.size();
        X = grid[0].size();
        for(size_t j = 0; j < grid[0].size(); j++)
        {
            for (size_t i = 0; i < grid.size(); i++)
            
            {
                if ((grid[i][j] == '1') && !visited[i][j])
                {
                    islands++;
                    search(i, j, grid);
                }
            }
        }
        return islands;
    }
};
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