<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>

int m, n;
bool vis[101][101];
vector<pair<int, int>> vp = {{1, 0}, {-1, 0}, {0, 1}, {0, -1}};
bool isvalid(int i, int j) {
    if (i >= 0 and i < n and j >= 0 and j < m)
        return true;
    return false;
}

void dfs(int s1, int s2, int& k, vector<vector<int>>& grid) {
    vis[s1][s2] = true;
    k++;
    for (int i = 0; i < 4; i++) {
        int j = s1 + vp[i].first;
        int l = s2 + vp[i].second;
        if (isvalid(j, l) and grid[j][l] == 1 and !vis[j][l]) {
            {
                dfs(j, l, k, grid);
            }
        }
    }
}
class Solution {
public:
    int maxAreaOfIsland(vector<vector<int>>& grid) {
        memset(vis, false, sizeof(vis));
        vector<int> vp;
        n = grid.size();
        m = grid[0].size();
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < m; j++) {
                if (grid[i][j] == 1 and !vis[i][j]) {
                    int k = 0;
                    dfs(i, j, k, grid);
                    vp.push_back(k);
                }
            }
        }
        sort(vp.begin(), vp.end(), greater<int>());
        if (vp.empty())
            return 0;
        else
            return vp[0];
    }
};
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