March punch card activity on the 15th day LeetCode 695 title: Islands maximum area (medium)

March punch card activity on the 15th day LeetCode 695 title: Islands maximum area (medium)

• Title: Given a two-dimensional array of non-null grid number 0 and 1, is an island formed of a combination of four directions (horizontal or vertical) 1 (representing the land). You can assume that the four edges of the two-dimensional matrix are surrounded by water. Find a given two-dimensional array in the largest island in the area. (If there are no islands, the area is returned to 0.)
  
• Problem solution approach: that is the way it should weekend, every weekend the title is not good to do, to make explanations Well, I just do not want to question ~~

class Solution {
    public int maxAreaOfIsland(int[][] grid) {
        int res = 0; 
        for (int i = 0; i < grid.length; i++) {
            for (int j = 0; j < grid[i].length; j++) {
                if (grid[i][j] == 1) {
                    res = Math.max(res, dfs(i, j, grid));
                }
            }
        } 
        return res;
    }
    // 每次调用的时候默认num为1，进入后判断如果不是岛屿，则直接返回0，就可以避免预防错误的情况。
    // 每次找到岛屿，则直接把找到的岛屿改成0，这是传说中的沉岛思想，就是遇到岛屿就把他和周围的全部沉默。
    // ps：如果能用沉岛思想，那么自然可以用朋友圈思想。有兴趣的朋友可以去尝试。
    private int dfs(int i, int j, int[][] grid) {
        if (i < 0 || j < 0 || i >= grid.length || j >= grid[i].length || grid[i][j] == 0) { 
            return 0;
        } 
        grid[i][j] = 0;
        int num = 1;
        num += dfs(i + 1, j, grid);
        num += dfs(i - 1, j, grid);
        num += dfs(i, j + 1, grid);
        num += dfs(i, j - 1, grid);
        return num;
        
    }
}

作者：mark-42
链接：https://leetcode-cn.com/problems/max-area-of-island/solution/biao-zhun-javadong-tai-gui-hua-jie-fa-100-by-mark-/
来源：力扣（LeetCode）
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