【重点】【DFS】1905. 统计子岛屿

题目

DFS

思路：
step1.先把grid2中是陆地但grid1中是海洋的岛变成海洋
step2.再统计grid2中岛屿的数量

Python

class Solution:
    def countSubIslands(self, grid1: List[List[int]], grid2: List[List[int]]) -> int:
        res = 0
        m, n = len(grid1), len(grid1[0])
        # step1.先把grid2中是陆地但grid1中是海洋的岛变成海洋
        for i in range(m):
            for j in range(n):
                if grid2[i][j] == 1 and grid1[i][j] == 0:
                    self.dfs(grid2, i, j)
        # step2.再统计grid2中岛屿的数量
        for i in range(m):
            for j in range(n):
                if grid2[i][j] == 1:
                    self.dfs(grid2, i, j)
                    res += 1
        
        return res

    def dfs(self, grid, i, j):
        if (i < 0 or i >= len(grid) 
            or j < 0 or j >= len(grid[0])
            or grid[i][j] == 0):
            return
        grid[i][j] = 0
        self.dfs(grid, i-1, j)
        self.dfs(grid, i+1, j)
        self.dfs(grid, i, j-1)
        self.dfs(grid, i, j+1)