BOJ1068 트리

blog.encrypted.gg/130 의 도움을 받아 풀 수 있었습니다.

from collections import deque
import sys

N = int(input())
parent = list(map(int, input().split()))
sibling = [[] for _ in range(N+1)]

root = -1
for i in range(N):
	if parent[i] == -1:
		root = i
	else:
		sibling[parent[i]].append(i)
del_node = int(input())

if del_node == root:
	print(0)
	sys.exit()

Q = deque()
Q.append(root)
cnt = 0
while Q:
	cur = Q.popleft()
	if len(sibling[cur]) == 0 or (len(sibling[cur]) == 1 and sibling[cur][0] == del_node):
		cnt += 1

	for next in sibling[cur]:
		if next != del_node:
			Q.append(next)


print(cnt)