F. Bear and Fair Set 题目连接: http://www.codeforces.com/contest/628/problem/F Description Limak is a grizzly bear. He is big and dreadful. You were chilling in the forest when you suddenly met him. It's very unfortunate for you. He will eat all your coo…

Educational Codeforces Round 40 F. Runner's Problem 题意: 给一个$ 3 * m \(的矩阵,问从\)(2,1)$ 出发 走到 \((2,m)\) 的方案数 \(mod 1e9 + 7\), 走的规则和限制如下: From the cell (i, j) you may advance to: (i - 1, j + 1) - only if i > 1, (i, j + 1), or (i + 1, j + 1) - only if i <…

https://codeforces.com/contest/1132/problem/F 思维 + 区间dp 题意 给一个长度为n的字符串(<=500),每次选择消去字符,连续相同的字符可以同时消去,问最少需要消去多少次 题解 定义dp[l][r]为区间[l,r]剩下一个字符所需要的最小次数 dp[l][r]=min(dp[l][i]+dp[i+1][r]+x) x为消去剩下两个字符所需要的次数,假如两个字符相同需要x=-1 代码 #include<bits/stdc++.h> #de…

https://codeforces.com/contest/1051/problem/F 题意 给一个带权联通无向图,n个点,m条边,q个询问,询问两点之间的最短路 其中 m-n<=20,1<=n,m<=1e5 思路 因为图一定联通,所以n-1<=m<=n+20 因为是求任意两点的最短路,所以直接暴力跑最短路是不行的,考虑选择性的跑最短路 因为是求两点之间的距离,所以可以往lca方面想 先跑一棵生成树出来,然后处理出每个点的lca,这样就可以求出任意两点的距离 然后就可以记…

F. Four Divisors 题目连接: http://www.codeforces.com/contest/665/problem/F Description If an integer a is divisible by another integer b, then b is called the divisor of a. For example: 12 has positive 6 divisors. They are 1, 2, 3, 4, 6 and 12. Let's def…

题目链接:http://codeforces.com/contest/837/problem/F 题意:如题QAQ 解法:参考题解博客:http://www.cnblogs.com/FxxL/p/7282909.html    由于新生成的m+1个数列第一个肯定为0,所以可以忽略掉,当作每次新生成的数列只拥有m个元素    来枚举一个例子,可以发现规律. 当a[] = {1,0,0,0,0}时,手动推出的矩阵如下: 可以发现对于这个矩阵显然是满足杨辉三角的,我们二分出一个值后可以直接利用组合数来…

F. Magic Matrix 题目连接: http://www.codeforces.com/contest/632/problem/F Description You're given a matrix A of size n × n. Let's call the matrix with nonnegative elements magic if it is symmetric (so aij = aji), aii = 0 and aij ≤ max(aik, ajk) for all…

F. Xors on Segments 题目连接: http://www.codeforces.com/contest/620/problem/F Description You are given an array with n integers ai and m queries. Each query is described by two integers (lj, rj). Let's define the function . The function is defined for o…

F. The Sum of the k-th Powers 题目连接: http://www.codeforces.com/contest/622/problem/F Description There are well-known formulas: , , . Also mathematicians found similar formulas for higher degrees. Find the value of the sum modulo 109 + 7 (so you shoul…

C. Bear and String Distance 题目连接: http://www.codeforces.com/contest/628/problem/C Description Limak is a little polar bear. He likes nice strings - strings of length n, consisting of lowercase English letters only. The distance between two letters is…