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200. Number of Islands

200. Number of Islands

作者: 冷殇弦 | 来源:发表于2017-10-10 22:04 被阅读0次

    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


    典型的DFS,markAsZero的函数很巧妙。

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

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