leetcode-191周赛-1466-重新规划路线

题目描述：

 

 

 

 

 

 提交：

class Solution:
    def minReorder(self, n: int, connections: List[List[int]]) -> int:
        connect = collections.defaultdict(set)
        c_set = set(tuple(i) for i in connections)
        for i, j in connections:
            connect[i].add(j)
            connect[j].add(i)
        res = [0]
        visited = set()
        visited.add(0)

        def dfs(i):
            for j in connect[i]:
                if j not in visited:
                    if (j, i) not in c_set:
                        res[0] += 1
                    visited.add(j)
                    dfs(j)

        dfs(0)
        return res[0]