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.)

Solution：DFS

思路：

Time Complexity: O(mn) Space Complexity: O(mn)

Solution Code：

class Solution {
    public int maxAreaOfIsland(int[][] grid) {
        int maxArea = 0;
        for (int i = 0; i < grid.length; i++) {
            for (int j = 0; j < grid[i].length; j++) {
                if (grid[i][j] == 1) {
                    int curArea = dfs(grid, i, j);
                    if (curArea > maxArea) {
                        maxArea = curArea;
                    }
                }
                
            }
        }
        return maxArea;
    }
    
    private int dfs(int[][] grid, int i, int j) {
        if (i < 0 || i >= grid.length || j < 0 || j >= grid[i].length) {
            return 0;
        }
        if (grid[i][j] == 0) {
            return 0;
        }
        grid[i][j] = 0; // set as visited
        return 1 + dfs(grid, i - 1, j) + dfs(grid, i + 1, j) + dfs(grid, i, j - 1) + dfs(grid, i, j + 1);
    }
}