Leetcode200 Number of Islands

题目描述

Given a 2d grid map of '1's (land) and '0's (water), count the number of islands. An island is surrounded by water and is formed by connecting adjacent lands horizontally or vertically. You may assume all four edges of the grid are all surrounded by water.

Example 1:

Input:
11110
11010
11000
00000

Output: 1

Example 2:

Input:
11000
11000
00100
00011

Output: 3

思路

深度优先搜索。首先找到岛（即找到1），然后深度优先查找他周围的是否存在岛屿，如果存在，将他沉没（即将1变为0）,递归搜索，直到char二维数组中的元素全部为0即将所有岛屿全部沉没。

代码

class Solution {
    public int numIslands(char[][] grid) {
        if(grid.length==0) return 0;
        int ans=0;
        for(int x=0;x<grid.length;x++){
            for(int y=0;y<grid[0].length;y++){
                if(grid[x][y]=='1'){
                    ans +=1;
                    search(grid,x,y);
                }
            }
        }
        return ans;
    }
    private static void search(char[][] grid, int x, int y){
        if(x<0||y<0||x>=grid.length||y>=grid[0].length||grid[x][y]=='0') 
            return;
        grid[x][y]='0';
        search(grid,x+1,y);
        search(grid,x,y+1);
        search(grid,x-1,y);
        search(grid,x,y-1);
    }
}