"""
출처:프로그래머스
https://school.programmers.co.kr/learn/courses/30/lessons/49191
"""

# 풀이 과정
from collections import defaultdict
from collections import deque


def solution(n, results):
    rank_win = defaultdict(set)
    rank_lose = defaultdict(set)

    for win, lose in results:
        rank_win[win].add(lose)
        rank_lose[lose].add(win)

    # 이긴 플레이 경로 재구성
    for player in range(1, n + 1):
        visit = [False] * (n + 1)
        visit[0] = True
        visit[player] = True

        q = deque([player])

        while q:
            opponent = q.popleft()
            visit[opponent] = True

            for i in rank_win[opponent]:
                if visit[i] == False:
                    q.append(i)
                    rank_win[player].add(i)

    # 진 플레이들 재구성
    for player in range(1, n + 1):
        visit = [False] * (n + 1)
        visit[0] = True
        visit[player] = True

        q = deque([player])

        while q:
            opponent = q.popleft()
            visit[opponent] = True

            for i in rank_lose[opponent]:
                if visit[i] == False:
                    q.append(i)
                    rank_lose[player].add(i)

    # 결과를 알 수 있는 플레이를 검색
    answer = 0

    for player in range(1, n + 1):
        if len(rank_win[player] | rank_lose[player]) == n - 1:
            answer += 1

    return answer