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]
原文：https://www.cnblogs.com/oldby/p/13023777.html