摘要：
You are given a tree (a connected undirected graph without cycles) of 𝑛n vertices. Each of the 𝑛−1n−1 edges of the tree is colored in either black o 阅读全文
摘要：
You went to the store, selling 𝑛n types of chocolates. There are 𝑎𝑖ai chocolates of type 𝑖i in stock. You have unlimited amount of cash (so you ar 阅读全文
摘要：
You are given a string 𝑠=𝑠1𝑠2…𝑠𝑛s=s1s2…sn of length 𝑛n, which only contains digits 11, 22, ..., 99. A substring 𝑠[𝑙…𝑟]s[l…r] of 𝑠s is a stri 阅读全文