HDU 4705 Y （2013多校10,1010题，简单树形DP）

Y

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 131072/131072 K (Java/Others)
Total Submission(s): 60    Accepted Submission(s): 20

Problem Description

 

Sample Input

4 1 2 1 3 1 4

 

Sample Output

1

Hint

1. The only set is {2,3,4}. 2. Please use #pragma comment(linker, "/STACK:16777216")

 

Source

2013 Multi-University Training Contest 10

 

Recommend

zhuyuanchen520

 

树形DP统计一遍就可以了。

/* ***********************************************
Author        :kuangbin
Created Time  :2013/8/22 12:27:59
File Name     :F:2013ACM练习2013多校101010.cpp
************************************************ */
#pragma comment(linker, "/STACK:1024000000,1024000000")
#include <stdio.h>
#include <string.h>
#include <iostream>
#include <algorithm>
#include <vector>
#include <queue>
#include <set>
#include <map>
#include <string>
#include <math.h>
#include <stdlib.h>
#include <time.h>
using namespace std;

const int MAXN = 100010;
struct Edge
{
    int to,next;
}edge[MAXN*2];
int head[MAXN],tot;
void init()
{
    memset(head,-1,sizeof(head));
    tot = 0;
}
void addedge(int u,int v)
{
    edge[tot].to = v;
    edge[tot].next = head[u];
    head[u] = tot++;
}


int num[MAXN];
int n;
long long ans;
void dfs(int u,int pre)
{
    num[u] = 1;
    int tmp = 0;
    for(int i = head[u];i!= -1;i = edge[i].next)
    {
        int v = edge[i].to;
        if(v == pre)continue;
        dfs(v,u);
        ans += (long long)tmp*num[v];
        num[u] += num[v];
        tmp += num[v];
    }
    ans += (long long)tmp*(n-num[u]);
}


int main()
{
    //freopen("in.txt","r",stdin);
    //freopen("out.txt","w",stdout);
    int u,v;
    while(scanf("%d",&n) == 1)
    {
        init();
        for(int i = 1;i < n;i++)
        {
            scanf("%d%d",&u,&v);
            addedge(u,v);
            addedge(v,u);
        }
        ans = 0;
        dfs(1,-1);
        long long tot = (long long)n*(n-1)*(n-2)/6;
        printf("%I64d
",tot-ans);
    }
    return 0;
}