题意 题目链接 \(n\)个点\(n\)条边的图,有多少种方法给边定向后没有环 Sol 一开始傻了,以为只有一个环...实际上N个点N条边还可能是基环树森林.. 做法挺显然的:找出所有的环,设第\(i\)个环的大小为\(w_i\) \(ans = 2^{N - \sum w_i} \prod (2^{w_i} - 2)\) 最后减掉的2是形成环的情况 #include<bits/stdc++.h> #define Pair pair<int, int> #define MP(x,…

D. Directed Roads   ZS the Coder and Chris the Baboon has explored Udayland for quite some time. They realize that it consists of n towns numbered from 1to n. There are n directed roads in the Udayland. i-th of them goes from town i to some other tow…

题目链接:http://codeforces.com/problemset/problem/711/D D. Directed Roads time limit per test 2 seconds memory limit per test 256 megabytes input standard input output standard output ZS the Coder and Chris the Baboon has explored Udayland for quite some…

D. Directed Roads time limit per test2 seconds memory limit per test256 megabytes inputstandard input outputstandard output ZS the Coder and Chris the Baboon has explored Udayland for quite some time. They realize that it consists of n towns numbered…

题目链接:D Directed Roads 题意:给出n个点和n条边,n条边一定都是从1~n点出发的有向边.这个图被认为是有环的,现在问你有多少个边的set,满足对这个set里的所有边恰好反转一次(方向反转),使得这个图里没有环. 思路:感觉关键是,n个点n条边,且每个点的出度为1,所以图里一定没有复环.想要使图里没环,对于每个连通块(点数为i)里的环(如果有环 点数为j),只要不是全翻和全不翻都是满足题意的set, 一共满足题意得set  即为 2^(i-j) * (2^j-2).所有的连通块…

题目链接: D. Directed Roads time limit per test 2 seconds memory limit per test 256 megabytes input standard input output standard output ZS the Coder and Chris the Baboon has explored Udayland for quite some time. They realize that it consists of n town…

D. Directed Roads time limit per test 2 seconds memory limit per test 256 megabytes input standard input output standard output ZS the Coder and Chris the Baboon has explored Udayland for quite some time. They realize that it consists of n towns numb…

Directed Roads 题目链接:http://codeforces.com/contest/711/problem/D dfs 刚开始的时候想歪了,以为同一个连通区域会有多个环,实际上每个点的出度为1,也就是说每个连通区域最多就只有一个环. 那么每一个连通区域的方法数就 = (2^环内边数-2)*(2^环外边数) [因为环内有两种情况形成圈,不可取], 总方法数 = 不同连通区域的方法数的乘积: 于是我把整个有向图先存储成无向图,用dfs判断该连通区域有没有环,再cls掉环外的边,之后再…

D. Directed Roads time limit per test 2 seconds memory limit per test 256 megabytes input standard input output standard output ZS the Coder and Chris the Baboon has explored Udayland for quite some time. They realize that it consists of ntowns numbe…

ZS the Coder and Chris the Baboon has explored Udayland for quite some time. They realize that it consists of n towns numbered from1 to n. There are n directed roads in the Udayland. i-th of them goes from town i to some other town ai (ai ≠ i). ZS th…