https://medium.com/@sylpid003/curcular-linked-list-%EB%A5%BC-%EC%82%AC%EC%9A%A9%ED%95%B4-%EC%BA%90%EB%9F%AC%EC%85%80-%EB%A7%8C%EB%93%A4%EA%B8%B0-fa7c7a92ebb3
