Ozon Tech Challenge 2020 (Div.1 + Div.2, Rated, T-shirts + prizes!) D. Kuroni and the Celebration

交互题。interactive problem。看得我一脸懵逼。看懂一个lca还以为要求lca，一看样例傻眼了。还好现在会了。

Codeforces Round621 (Div. 1 + Div. 2) D. Cow and Fields

一道图论题

Educational Codeforces Round 78 (Rated for Div. 2) D. Segment Tree

关于STL，我想说，它太妙了。