传送门:https://codeforces.com/contest/110/problem/E 题意:给你一颗树,节点与节点之间的边有一个边权,定义只由4和7组成的数字是幸运数字,现在要你求一共有多少条路径,使得节点u->v之间至少存在一条边为幸运数字 题解:树形dp+容斥,我们要找有多少条路径上至少存在一条幸运边,那么我们就可以找到所有的不含幸运路径的边然后用所有路径和减去不含幸运路径的边即可 1,每次输入边权的时候处理边权是否为幸运数字,如果是,那么为1,否则为0 2,dfs处理,如果边权…

Problem - D - Codeforces  Fix a Tree 看完第一名的代码,顿然醒悟... 我可以把所有单独的点全部当成线,那么只有线和环. 如果全是线的话,直接线的条数-1,便是操作数. 如果有环和线,环被打开的同时,接入到线上.那就是线和环的总数-1. 如果只有环的话,把所有的环打开,互相接入,共需n次操作. #include <cstdio> #include <algorithm> using namespace std; ; int cur[maxn];…

赶脚官方题解写得挺清楚的说,=_= 注意数据范围用long long,否则会溢出. #include <iostream> #include <cstdio> #include <algorithm> #include <cstring> #include <vector> using namespace std; + ; int n; vector<int> G[maxn], C[maxn]; inline int lucky(in…

Lucky Ticket Time Limit:2000MS     Memory Limit:262144KB     64bit IO Format:%I64d & %I64u Submit Status Practice CodeForces 146A Description Petya loves lucky numbers very much. Everybody knows that lucky numbers are positive integers whose decimal…

Petya loves lucky numbers. We all know that lucky numbers are the positive integers whose decimal representations contain only the lucky digits 4 and 7. For example, numbers 47, 744, 4 are lucky and 5, 17, 467 are not. One day Petya encountered a tre…

题目链接:http://codeforces.com/problemset/problem/765/E $DFS子$树进行$DP$ 大概分以下几种情况: 1.为叶子,直接返回. 2.长度不同的路径长度只有一条,显然可以合并成这一条的长度. 3.长度不同的路径长度有两条,并且这个点为根,显然可以合并成这两条的长度和. 4.其他的都不合法. 注意:事实上如果第一次$DP$之后不合法要考虑换根再做一次 #include<iostream> #include<cstdio> #includ…

链接:http://codeforces.com/problemset/problem/570/D D. Tree Requests time limit per test 2 seconds memory limit per test 256 megabytes input standard input output standard output Roman planted a tree consisting of n vertices. Each vertex contains a low…

Lucky Sum Time Limit: 2000ms Memory Limit: 262144KB This problem will be judged on CodeForces. Original ID: 121A64-bit integer IO format: %I64d      Java class name: (Any)     Petya loves lucky numbers. Everybody knows that lucky numbers are positive…

Propagating tree Time Limit: 2000ms Memory Limit: 262144KB This problem will be judged on CodeForces. Original ID: 383C64-bit integer IO format: %I64d      Java class name: (Any)   Iahub likes trees very much. Recently he discovered an interesting tr…

time limit per test2 seconds memory limit per test256 megabytes inputstandard input outputstandard output Roman planted a tree consisting of n vertices. Each vertex contains a lowercase English letter. Vertex 1 is the root of the tree, each of the n …