原题链接Ahttps://codeforces.com/contest/1999/problem/A800Bhttps://qoj.ac/contest/1794/problem/9310Chttps://codeforces.com/problemset/problem/2008/D1100Dhttps://qoj.ac/contest/1485/problem/8081Ehttps://codeforces.com/contest/2002/problem/B