逃生问题：

思路：根结点左右子树的最大结点数。本地测试通过，提交不通过，不知道哪错了，大佬们帮忙看看

import collections
import sys
n = int(input())
edges = []
while True:
    a = []
    s = input()
    if s != "":
        for x in s.split():
            a.append(int(x))
        edges.append(a)
    else:
        break
graph = collections.defaultdict(set)
for u, v in edges:
    graph[u].add(v)
    graph[v].add(u)


def dfs(graph, node, visited):
    count = 1
    visited[node] = True
    for child in graph[node]:
        if not visited[child]:
            count += dfs(graph, child, visited)
    return count


res = 0
visited = [False] * (n + 1)
visited[1] = True
for child in graph[1]:
    nodeNums = dfs(graph, child, visited)
    if res < nodeNums:
        res = nodeNums
sys.stdout.write(str(res)+"\n")