200. Number of Islands

佚名 6年前 (2019-04-16) 随笔 1952人围观抢沙发百度已收录

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:

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Input:
11110
11010
11000
00000

Output: 1

Example 2:

用DFS，遇到1就ans++，然后搜索所有他的1邻居直到搜不到了，这时代表有一个island,

接下来继续搜索，原理同上

class Solution {
    public int numIslands(char[][] grid) {
       int m = grid.length;
        if(m == 0) return 0;
        int n = grid[0].length;
        int ans = 0;
        for(int i = 0; i < m; i++){
            for(int j = 0; j < n; j++){
                if (grid[i][j]=='1'){
                    ans++;
                    DFS(grid,m,n,i,j);
                }
            }
        }
        return ans;
    }
    private void DFS(char[][] grid, int m, int n, int i, int j){
        if(i < 0|| j < 0|| i >= m || j >=n|| grid[i][j] == '0') return;
        grid[i][j] = '0';
        DFS(grid,m,n,i+1,j);
        DFS(grid,m,n,i-1,j);
        DFS(grid,m,n,i,j+1);
        DFS(grid,m,n,i,j-1);
    }
}