<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:
    int maxAreaOfIsland(vector<vector<int>>& grid) {
        
        int maxArea = 0;
        int ROWS = grid.size();
        int COLS = grid[0].size();
        unordered_set<int> visited;

        for(int i = 0; i < ROWS; ++i) {
            for(int j = 0; j < COLS; ++j) {
                int idx = i * COLS + j;
                if(grid[i][j] == 1 && visited.count(idx) == 0) {
                    maxArea = max(maxArea,dfs(grid,i,j,visited));
                }
            }
        }

        return maxArea;

    }

    int dfs(vector<vector<int>>& grid, int currRow, int currCol, unordered_set<int>& visited) {
        int ROWS = grid.size();
        int COLS = grid[0].size();
        int idx = currRow * COLS + currCol;

        if(currRow < 0 || currCol < 0 || currRow >= ROWS || currCol >= COLS || 
            grid[currRow][currCol] == 0 || visited.count(idx)) {
                return 0;
        }

        int count = 0;
        if(grid[currRow][currCol] == 1) {
            ++count;
        }

        visited.insert(idx);
        count += dfs(grid,currRow-1,currCol,visited);
        count += dfs(grid,currRow+1,currCol,visited);
        count += dfs(grid,currRow,currCol-1,visited);
        count += dfs(grid,currRow,currCol+1,visited);

        return count;
    }
};
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