hdu 4118 树形dp

思路：其实就是让每一条路有尽量多的人走。

#pragma comment(linker, "/STACK:1024000000,1024000000")

#include<map>

#include<set>

#include<cmath>

#include<queue>

#include<cstdio>

#include<vector>

#include<string>

#include<cstdlib>

#include<cstring>

#include<iostream>

#include<algorithm>

#define Maxn 100010

#define Maxm 100010

#define LL __int64

#define Abs(x) ((x)>0?(x):(-x))

#define lson(x) (x<<1)

#define rson(x) (x<<1|1)

#define inf 0x7fffffff

#define Mod 1000000007

using namespace std;

struct Edge{

    int u,v,next;

    LL val;

}edge[Maxm*2];

LL dp[Maxn],sum[Maxn],n;

int e,vi[Maxn],head[Maxn];

void init()

{

    memset(dp,0,sizeof(dp));

    memset(sum,0,sizeof(sum));

    memset(head,-1,sizeof(head));

    memset(vi,0,sizeof(vi));

    e=0;

}

void add(int u,int v,LL val)

{

    edge[e].u=u,edge[e].v=v,edge[e].val=val,edge[e].next=head[u],head[u]=e++;

    edge[e].u=v,edge[e].v=u,edge[e].val=val,edge[e].next=head[v],head[v]=e++;

}

void dfs(int u)

{

    int i,v;

    sum[u]=1;

    dp[u]=0;

    vi[u]=1;

    for(i=head[u];i!=-1;i=edge[i].next){

        v=edge[i].v;

        if(vi[v]) continue;

        dfs(v);

        LL num=min(sum[v],n-sum[v]);

        dp[u]+=dp[v]+num*edge[i].val*2;

        sum[u]+=sum[v];

    }

   // cout<<u<<" "<<dp[u]<<endl;

}

int main()

{

    int t,i,j,u,v,Case=0;

    LL val;

    scanf("%d",&t);

    while(t--){

        init();

        scanf("%I64d",&n);

        for(i=1;i<n;i++){

            scanf("%d%d%I64d",&u,&v,&val);

            add(u,v,val);

        }

        dfs(1);

        printf("Case #%d: %I64d\n",++Case,dp[1]);

    }

    return 0;

}