200.md

200. Number of Islands

难度: Medium

刷题内容

原题连接

• https://leetcode.com/problems/number-of-islands/description/

内容描述

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

解题方案

思路 1

厉害的解法：Sink and count the islands.

就是说从(0,0)这个点开始，只要一碰到1就将我们最终island数加1，并且同时将其周围临近的所有1全部都变成0，这样后面就不会重复计算了

class Solution(object):
    def numIslands(self, grid):
        """
        :type grid: List[List[str]]
        :rtype: int
        """
        def sink(i, j):
            if 0 <= i < len(grid) and 0 <= j < len(grid[0]) and grid[i][j] == '1':
                grid[i][j] = '0'
                map(sink, (i+1, i-1, i, i), (j, j, j+1, j-1))
                return 1
            return 0
        return sum(sink(i, j) for i in range(len(grid)) for j in range(len(grid[0])))