<p>You are given an <code>m x n</code> binary matrix <code>grid</code>. An island is a group of <code>1</code>&#39;s (representing land) connected <strong>4-directionally</strong> (horizontal or vertical.) You may assume all four edges of the grid are surrounded by water.</p>

<p>The <strong>area</strong> of an island is the number of cells with a value <code>1</code> in the island.</p>

<p>Return <em>the maximum <strong>area</strong> of an island in </em><code>grid</code>. If there is no island, return <code>0</code>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2021/05/01/maxarea1-grid.jpg" style="width: 500px; height: 310px;" />
<pre>
<strong>Input:</strong> grid = [[0,0,1,0,0,0,0,1,0,0,0,0,0],[0,0,0,0,0,0,0,1,1,1,0,0,0],[0,1,1,0,1,0,0,0,0,0,0,0,0],[0,1,0,0,1,1,0,0,1,0,1,0,0],[0,1,0,0,1,1,0,0,1,1,1,0,0],[0,0,0,0,0,0,0,0,0,0,1,0,0],[0,0,0,0,0,0,0,1,1,1,0,0,0],[0,0,0,0,0,0,0,1,1,0,0,0,0]]
<strong>Output:</strong> 6
<strong>Explanation:</strong> The answer is not 11, because the island must be connected 4-directionally.
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> grid = [[0,0,0,0,0,0,0,0]]
<strong>Output:</strong> 0
</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;= 50</code></li>
	<li><code>grid[i][j]</code> is either <code>0</code> or <code>1</code>.</li>
</ul>

class Solution {
public:

    bool vis[2600][2600];
    vector<pair<int, int>> d = {{0, 1}, {0, -1}, {-1, 0}, {1, 0}};

    int n, m;

    bool valid(int i, int j)
    {
        if(i < 0 || i >= n || j < 0 || j >=m)
            return false;
        else
            return true;
    }

    int ans = 0;
    int count = 0;

    void dfs(int si, int sj, vector<vector<int>>& grid)
    {
        vis[si][sj] = true;
        count++;

        for(int i = 0; i < 4; i++)
        {
            int ci = si + d[i].first;
            int cj = sj + d[i].second;
            
            if(valid(ci, cj) == true && vis[ci][cj] == false && grid[ci][cj] != 0)
            {
                dfs(ci, cj, grid);
            }
        }
    }

    int maxAreaOfIsland(vector<vector<int>>& grid) 
    {
        memset(vis, false, sizeof(vis));

        n = grid.size();
        m = grid[0].size();


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