https://www.acmicpc.net/problem/2170
https://www.acmicpc.net/problem/2003
https://www.acmicpc.net/problem/1931
https://www.acmicpc.net/problem/11047
https://www.acmicpc.net/problem/1541
https://www.acmicpc.net/problem/10816
https://www.acmicpc.net/problem/2110
알고리즘 트레이닝 4장 내용 문제들
정렬과 탐색 이진 탐색은 직접 구현해야했음
병합정렬도 구현해봄