<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:
    void
    dfs(vector<vector<int>> &grid, vector<vector<int>> &visited, const int &r, const int &c, int &cnt, int delR[],
        int delC[],
        const int &n, const int &m) {
        visited[r][c] = 1;

        cnt++;

        for (int i = 0; i < 4; i++) {
            int rw = r + delR[i];
            int cw = c + delC[i];

            if (rw >= 0 && rw < n && cw >= 0 && cw < m && !visited[rw][cw] && grid[rw][cw] == 1) {
                dfs(grid, visited, rw, cw, cnt, delR, delC, n, m);
            }
        }
    }

    int maxAreaOfIsland(vector<vector<int>> &grid) {
        const int n = static_cast<int>(grid.size());
        const int m = static_cast<int>(grid[0].size());

        vector<vector<int>> visited(n, vector<int>(m, 0));
        int mx = 0;

        int delR[4] = {-1, 0, 1, 0};
        int delC[4] = {0, 1, 0, -1};

        for (int i = 0; i < n; i++) {
            for (int j = 0; j < m; j++) {
                int cnt = 0;

                if (!visited[i][j] && grid[i][j] == 1) {
                    dfs(grid, visited, i, j, cnt, delR, delC, n, m);
                    mx = max(mx, cnt);
                }
            }
        }

        return mx;
    }
};
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