树状结构查询

import functools
import collections
import math
from itertools import combinations
from re import match
import copy 
from collections import defaultdict
 
n = int(input())
relation = {}
for i in range(n):
    params = [x for x in input().split(" ")]
    a = params[0]
    b = params[1]
    if b not in relation:
        relation[b] = set([])
    relation[b].add(a)
target = input()
queue = list(relation[target])
result = []
while len(queue) > 0:
    vals = queue[0]
    queue.pop(0)
    result.append(vals)
    if vals in relation:
        for x in list(relation[vals]):
            queue.append(x)
 
result = sorted(result,key=lambda x: x ,reverse=False)
output_str = ""
for ele in result:
    output_str += ele + "\n"
print(output_str)