https://programmers.co.kr/learn/courses/30/lessons/42884
def solution(routes):
routes.sort(key=lambda x: x[1])
visited = [False] * len(routes)
count = 0
for i in range(len(routes)):
if not visited[i]:
visit(routes, visited, routes[i][1])
count += 1
return count
def visit(routes, visited, t):
for i in range(len(routes)):
s, e = routes[i]
if s <= t <= e:
visited[i] = True