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]

這道題有點像 word search的簡化版. 每遇到'1'後, 開始向四個方向 遞歸搜尋. 搜到後變為'0', 因為相鄰的屬于一個island. 然後開始繼續找下一個'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);
    }
}