<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:
    bool check(int i , int j , int n , int m , vector<vector<char>>& grid, vector<vector<bool>> &vis){
        if(i < 0 || i >= n || j < 0 || j >= m || grid[i][j] == '0' || vis[i][j] == true){
            return false;
        }else{
            return true;
        }
    }
    void dfs(int i , int j ,vector<vector<char>>& grid, vector<vector<bool>> &vis , int n , int m){
        vis[i][j] = true;
        
        // check all the four directions
        // up( i - 1 , j)
        if(check(i - 1 , j,  n , m , grid , vis) == true){
            dfs(i - 1, j ,grid, vis , n ,m );
        }
        // down (i + 1 , j)
        if(check(i + 1, j , n , m , grid, vis) == true){
            dfs(i + 1, j ,grid, vis, n , m);
        }
        // right (i, j + 1)
        if(check(i , j+ 1, n , m , grid, vis) == true){
            dfs(i ,j + 1,grid , vis, n ,m );
        }
        // left (i,  j -1)
        if(check(i , j - 1 , n , m , grid , vis) == true){
            dfs(i , j - 1, grid , vis, n , m);
        }
    }
    int numIslands(vector<vector<char>>& grid) {
        int ans = 0;
        int n = grid.size() , m = grid[0].size();
        vector<vector<bool>> vis( n , vector<bool>(m , false));

        for(int i = 0 ; i < n ; i++){
            for(int j = 0 ; j < m  ; j++){
                if(grid[i][j] == '1' && vis[i][j] == false){
                    dfs(i , j , grid, vis , n , m);
                    ans = ans + 1;
                }
            }
        }
        return ans;
    }
};
10903