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树包含N个点和N-1条边。树的边有2中颜色红色(‘r’)和黑色（‘b’)。给出这N-1条边的颜色，求有多少节点的三元组(a,b,c)满足：节点a到节点b、节点b到节点c、节点c到节点a的路径上，每条路径都至少有一条边是红色的。注意(a,b,c), (b,a,c)以及所有其他排列被认为是相同的三元组。输出结果对1000000007取余的结果。找补集，快乐容斥一下就好了#include<...

题目描述Description Stancu likes space travels but he is a poor software developer and will never be able to buy his own spacecraft. That is why he is preparing to steal the spacecraft of Petru. There is only one problem – Petru has locked the spacec

#include<bits/stdc++.h>#define re return#define inc(i,l,r) for(register int i=l;i<=r;++i)using namespace std;char buf[1<<21],*p1,*p2;inline int gc(){re p1==p2 and(p2=(p1=buf)+f...