摘要：A. Vika and Her Friends Vika and her friends went shopping in a mall, which can be represented as a rectangular grid of rooms with sides of length $n$ 阅读全文

摘要：C. Particles You have discovered $n$ mysterious particles on a line with integer charges of $c_1,\dots,c_n$. You have a device that allows you to perf 阅读全文