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D题 : Division by Two and Permutation题意：首先我晚上写这道题的时候是没有读懂题意的/wu，后来听了别人的讲解才明白是咋回事。现在给出一个长度为n的字符串str和一个整数k。k代表的是有k种颜色，要求每种颜色必须要至少要在给出的字符串上涂一个字符。（其他字符可以不涂色）然后将所有颜色单独任意排列，每个颜色排列的字符串必须是回文串。现在让你求出k种颜色中的回文串最短的字符串的最大值。即 使最短的回文串尽量大。思路：首先统计出所有的对数，对所有字符除对数外的统计

C. Number of Pairstime limit per test2 secondsmemory limit per test256 megabytesinputstandard inputoutputstandard outputYou are given an array a of n integers. Find the number of pairs (i,j) (1≤i<j≤n) where the sum of ai+aj is greater than or equal

Baby Ehab Partitions AgainBaby Ehab was toying around with arrays. He has an array a of length n. He defines an array to be good if there’s no way to partition it into 2 subsequences such that the sum of the elements in the first is equal to the sum of th

一 Balance the Bits 传送门A sequence of brackets is called balanced if one can turn it into a valid math expression by adding characters ‘+’ and ‘1’. For example, sequences ‘(())()’, ‘()’, and ‘(()(()))’ are balanced, while ‘)(’, ‘(()’, and ‘(()))(’ a