CF Rating+200
排序+优先队列 https://codeforces.com/problemset/problem/1665/C
数学推导 https://codeforces.com/problemset/problem/1670/D
数学推导+出现DP https://codeforces.com/problemset/problem/1637/D
专题DP
牛客周赛 牛客竞赛