https://adrianmejia.com/data-structures-time-complexity-for-beginners-arrays-hashmaps-linked-lists-stacks-queues-tutorial/
https://medium.com/@jwyeom63/%EB%B2%88%EC%97%AD-%EC%A0%95%EA%B7%9C%ED%91%9C%ED%98%84%EC%8B%9D%EC%9C%BC%EB%A1%9C-5%EC%9D%BC-%EA%B1%B8%EB%A6%AC%EB%8A%94-%EC%9E%91%EC%97%85-15%EB%B6%84%EB%A7%8C%EC%97%90-%EB%81%9D%EB%82%B4%EA%B8%B0-2e615a907048
