BOJ Series
https://www.acmicpc.net/problem/1000
https://www.acmicpc.net/problem/1001
https://www.acmicpc.net/problem/1032
https://www.acmicpc.net/problem/2042
https://www.acmicpc.net/problem/2559
https://www.acmicpc.net/problem/6549
https://www.acmicpc.net/problem/9372
https://www.acmicpc.net/problem/9934
https://www.acmicpc.net/problem/10868
https://www.acmicpc.net/problem/11505
https://www.acmicpc.net/problem/11656
https://www.acmicpc.net/problem/13904
https://www.acmicpc.net/problem/14003
https://www.acmicpc.net/problem/14428
https://www.acmicpc.net/problem/15681