有趣（不会）的题

https://ac.nowcoder.com/acm/contest/44042/A   （暴力的链表并查集）

https://atcoder.jp/contests/abc269/tasks/abc269_c   （01序列的01子集）C. Submask

https://atcoder.jp/contests/abc268/tasks/abc268_c   （转圈题）C-Chinese Restaurant

https://atcoder.jp/contests/abc270/tasks/abc270_c   （dfs的路径回溯）C. Simple path

 https://atcoder.jp/contests/abc267/tasks/abc267_b   （两个柱子之间是不是全空的，读题很难读）B-Split?

https://atcoder.jp/contests/abc266/tasks/abc266_c（凸多边形的判定）C - Convex Quadrilateral

https://atcoder.jp/contests/abc264/tasks/abc264_c   （o(2^n)求子矩阵）C - Matrix Reducing