<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:

    int x[4] = {-1, 0, 1, 0};
    int y[4] = {0, 1, 0, -1};

    map<pair<int, int>, bool> visited;


    int m,n;

    void dfs(int i, int j, vector<vector<char>>& grid) {
        visited[pair(i, j)] = true;

        for (int k = 0; k < 4; k++) {
            int r = i + x[k];
            int c = j + y[k];

            if (r >= 0 && r < m && c >= 0 && c < n && grid[r][c] == '1' && !visited[pair(r,c)]){
                dfs(r,c, grid);
            }
        }
    }
    int numIslands(vector<vector<char>>& grid) {
        m = grid.size();
        n = grid[0].size();

        int numOfLand = 0;
        int ans = 0;
        for (int i = 0; i < m; i++) {
            for (int j = 0; j < n; j++) {
                visited.insert(pair(make_pair(i, j), false));
                if (grid[i][j] == '1') {
                    numOfLand++;
                }
            }
        }
        if (numOfLand == 0)
            return 0;
        for (int i = 0; i < m; i++) {
            for (int j = 0; j < n; j++) {
                if (grid[i][j] == '1' && !visited[pair(i, j)]) {
                    ans++;
                    dfs(i, j, grid);
                }
                //cout<<"visited["<<i<<"]["<<j<<"] = "<<visited[pair(i, j)]<<" ";

            }
            cout<<endl;
        }
        
        return ans;
    }
};
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