bzoj-3522 Hotel

#include<stdio.h>
#include<string.h>
#include<algorithm>
#define N 5100
using namespace std;
typedef long long ll;
int next[N<<1],to[N<<1],head[N],ce;
int deep[N],hash[N],last;
ll f1[N],f2[N];
void add(int x,int y)
{
	to[++ce]=y;
	next[ce]=head[x];
	head[x]=ce;
}
void dfs(int x,int pre)
{
	deep[x]=deep[pre]+1;
	hash[deep[x]]++;
	last=max(last,deep[x]);
	for(int i=head[x];i;i=next[i])
	{
		if(to[i]!=pre)
		{
			dfs(to[i],x);
		}
	}
}
int main()
{
	int n,m,i,j,k,x,y;
	ll ans;
	scanf("%d",&n);
	for(i=1;i<n;i++)
	{
		scanf("%d%d",&x,&y);
		add(x,y),add(y,x);
	}
	for(i=1,ans=0;i<=n;i++)
	{
		deep[i]=0;
		memset(f1,0,sizeof(f1));
		memset(f2,0,sizeof(f2));
		for(k=head[i];k;k=next[k])
		{
			memset(hash,0,sizeof(int)*(last+5));
			last=0;
			dfs(to[k],i);
			for(j=1;j<=last;j++)
			{
				ans+=hash[j]*f2[j];
				f2[j]+=f1[j]*hash[j];
				f1[j]+=hash[j];
			}	
		}
	}
	printf("%lld\n",ans);
	return 0;
}

bzoj-3522 Hotel

原文：http://blog.csdn.net/ww140142/article/details/49177345