leetcode 200 : Number of Islands

Number of Islands

Total Accepted: 8305 Total Submissions: 38192

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:

11110
11010
11000
00000      

Answer: 1

Example 2:

11000
11000
00100
00011      

Answer: 3

[思路]

这道题有点像 word search的简化版. 每遇到'1'后, 开始向四个方向 递归搜索. 搜到后变为'0', 因为相邻的属于一个island. 然后开始继续找下一个'1'.

[CODE]

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