200. 岛屿的个数

问题描述

给定一个由 '1'（陆地）和 '0'（水）组成的的二维网格，计算岛屿的数量。一个岛被水包围，并且它是通过水平方向或垂直方向上相邻的陆地连接而成的。你可以假设网格的四个边均被水包围。

示例 1:

输入:
11110
11010
11000
00000

输出: 1

示例 2:

输入:
11000
11000
00100
00011

输出: 3

解决方案

import collections


class Solution(object):
    def is_valid(self, grid, r, c):
        m, n = len(grid), len(grid[0])
        if r < 0 or c < 0 or r >= m or c >= n:
            return False
        return True

    def numIsLandsBFS(self, grid):
        if not grid or not grid[0]:
            return 0
        m, n = len(grid), len(grid[0])
        count = 0
        for i in range(m):
            for j in range(n):
                if grid[i][j] == "1":
                    self.bfs(grid, i, j)
                    count += 1
        return count

    def bfs(self, grid, r, c):
        queue = collections.deque()
        queue.append((r, c))
        grid[r][c] = "0"
        while queue:
            directions = [(0, 1), (0, -1), (-1, 0), (1, 0)] # 方向键
            r, c = queue.popleft()
            for d in directions:
                nr, nc = r + d[0], c + d[1]
                if self.is_valid(grid, nr, nc) and grid[nr][nc] == '1':
                    queue.append((nr, nc))
                    grid[nr][nc] = '0'


if __name__ == "__main__":
    s = Solution()
    my_sea = [["1", "1", "1", "1", "0"], ["1", "1", "1", "1", "0"], ["1", "1", "1", "1", "0"],
              ["1", "1", "1", "1", "0"]]
    num = s.numIsLandsBFS(my_sea)
    print(num)