프로그래머스 순위 (파이썬, set)

def solution(n, results):
    answer = 0
    
    win={x:set() for x in range(1,n+1) }
    lose={x:set() for x in range(1,n+1)}
   
    for winner,loser in results:
        win[winner].add(loser)
        lose[loser].add(winner)
        
    for i in range(1,n+1):
        for winner in lose[i]:
            win[winner].update(win[i])
        
        for loser in win[i]:
            lose[loser].update(lose[i])

    for i in range(1,n+1):
        if len(lose[i])+len(win[i])==n-1:
            answer+=1
    return answer