# 0695. Max Area of Island

<https://leetcode.com/problems/max-area-of-island>

## Description

You are given an `m x n` binary matrix `grid`. An island is a group of `1`'s (representing land) connected **4-directionally** (horizontal or vertical.) You may assume all four edges of the grid are surrounded by water.

The **area** of an island is the number of cells with a value `1` in the island.

Return *the maximum **area** of an island in* `grid`. If there is no island, return `0`.

**Example 1:**

![](https://assets.leetcode.com/uploads/2021/05/01/maxarea1-grid.jpg)

```
**Input:** 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]]
**Output:** 6
**Explanation:** The answer is not 11, because the island must be connected 4-directionally.
```

**Example 2:**

```
**Input:** grid = [[0,0,0,0,0,0,0,0]]
**Output:** 0
```

**Constraints:**

* `m == grid.length`
* `n == grid[i].length`
* `1 <= m, n <= 50`
* `grid[i][j]` is either `0` or `1`.

## ac

```java
class Solution {
    int cnt = 0;
    int max = 0;
    public int maxAreaOfIsland(int[][] grid) {
        // edge cases
        if (grid.length == 0 || grid[0].length == 0) {
            return 0;
        }

        for (int r = 0; r < grid.length; r++) {
            for (int c = 0; c < grid[0].length; c++) {
                if (grid[r][c] == 1) {
                    cnt = 0;
                    helper(grid, r, c);
                }
            }
        }

        return max;
    }

    private void helper(int[][] grid, int r, int c) {
        // exit
        if (r < 0 || r >= grid.length || c < 0 || c >= grid[0].length
           || grid[r][c] == 0) {
            return;
        }

        grid[r][c] = 0; // mark visted
        cnt++;
        max = Math.max(max, cnt);

        // check neighbors
        helper(grid, r+1, c);
        helper(grid, r-1, c);
        helper(grid, r, c+1);
        helper(grid, r, c-1);
    }
}
```


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