방에 들어갔다 나왔다. def solution(enter, leave): n = len(enter) answer = [0] * (n+1) enter_idx = 0 leave_idx = 0 room = set() while leave_idx < n: if leave[leave_idx] in room: room.discard(leave[leave_idx]) leave_idx += 1 continue if enter[enter_idx] not in room: for man in room: answer[man] += 1 answer[enter[enter_idx]] = len(room) room.add(enter[enter_idx]) enter_idx += 1 return answer[1:]