题目戳这里. 这道题目纯粹是考思维. 若\(2N \le M\),由于答案肯定是\(s,s+d,\dots,s+(N-1)d\),我们任意枚举两个数\(a,b\),不妨设\(b\)在数列中出现在\(a\)后面\(k\)位,设\(g = b-a\),则\(g\)这个差在所有数出现刚好\(N-K\)次.我们任取个\(g\),用二分或哈希求个差出现次数,就可以得知\(k\)了,然后\(d = gk^{-1}\).在检验数列中有\(a\)的公差为\(d\)的等差数列是否存在即可. 若\(2N > M\)…

A. Timofey and a tree 题意:给一棵树,要求判断是否存在一个点,删除这个点后,所有连通块内颜色一样.$N,C \le 10^5$ 想法:这个叫换根吧.先求出一个点合法即其儿子的子树内颜色一样,非该点子树的点颜色都一样.可以用DFS序解决. #include< cstdio > typedef long long ll; template inline void read(T&x) { x=0;bool f=0;char c=getchar(); while((c&l…

Each New Year Timofey and his friends cut down a tree of n vertices and bring it home. After that they paint all the n its vertices, so that the i-th vertex gets color ci. Now it's time for Timofey birthday, and his mother asked him to remove the tre…

Young Timofey has a birthday today! He got kit of n cubes as a birthday present from his parents. Every cube has a number ai, which is written on it. Timofey put all the cubes in a row and went to unpack other presents. In this time, Timofey's elder…

题目大意: 告诉你一个长度为n的等差数列在模m意义下的乱序值(互不相等),问是否真的存在满足条件的等差数列,并尝试构造任意一个这样的数列. 思路: 首先我们可以有一个结论: 两个等差数列相等,当且仅当数字和与平方和分别相等. 首先求出一开始的数字和和平方和. 然后我们枚举每一个数作为首项的情况,求出这个数作为首项以后的数字和和平方和,根据数字和求出公差,然后用平方和检验一下. 然而这样并不能保证一定正确,但至少有大概率是正确的,我们可以O(n)的时间检验一下. 注意特判n=m的情况. #incl…

地址:http://codeforces.com/contest/764/problem/D 题目: D. Timofey and rectangles time limit per test 2 seconds memory limit per test 256 megabytes input standard input output standard output One of Timofey's birthday presents is a colourbook in a shape o…

地址:http://codeforces.com/contest/764/problem/C 题目: C. Timofey and a tree time limit per test 2 seconds memory limit per test 256 megabytes input standard input output standard output Each New Year Timofey and his friends cut down a tree of n vertices…

地址:http://codeforces.com/contest/764/problem/B 题目: B. Timofey and cubes time limit per test 1 second memory limit per test 256 megabytes input standard input output standard output Young Timofey has a birthday today! He got kit of n cubes as a birthd…

time limit per test1 second memory limit per test256 megabytes inputstandard input outputstandard output Young Timofey has a birthday today! He got kit of n cubes as a birthday present from his parents. Every cube has a number ai, which is written on…

time limit per test2 seconds memory limit per test256 megabytes inputstandard input outputstandard output Each New Year Timofey and his friends cut down a tree of n vertices and bring it home. After that they paint all the n its vertices, so that the…