［LeetCode］Max Area of Island 岛屿的最大面积

链接：https://leetcode.com/problems/max-area-of-island/description/
难度：Easy
题目：695. Max Area of Island
Given a non-empty 2D array grid of 0's and 1's, 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.

Find the maximum area of an island in the given 2D array. (If there is no island, the maximum area is 0.)
Example 1:

[[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]]
 Given the above grid, return 6. Note the answer is not 11, because the island must be connected 4-directionally.

Example 2:

[[0,0,0,0,0,0,0,0]]
Given the above grid, return 0.

Note:

• The length of each dimension in the given grid does not exceed 50.

翻译：给定非空2维矩阵，元素为0或1，1代表陆地，四个方向中若有陆地相连，则代表岛屿，求最大岛屿的面积。

思路：用递归的方法深度优先搜索计算岛屿面积。遍历整个矩阵求最大面积。

参考代码：
Java

class Solution {
    public int maxAreaOfIsland(int[][] grid) {
        int maxArea = 0;
        for(int i=0; i< grid.length; i++){
            for(int j=0; j<grid[0].length; j++){
                if(grid[i][j] != 0){
                    maxArea = Math.max(maxArea, areaOfIsland(grid, i, j));
                }
            }
        }
        return maxArea;
    }
    
    public int areaOfIsland(int[][] grid, int i, int j) {
        if(i>=0 && j>=0 && i<grid.length && j<grid[0].length && grid[i][j] == 1){
            grid[i][j] = 0;
            return 1+areaOfIsland(grid, i+1, j) + areaOfIsland(grid, i-1, j)+areaOfIsland(grid, i, j+1)+areaOfIsland(grid, i, j-1);
        }
        return 0;
    }
}```