zoj 3659

题目链接：http://acm.zju.edu.cn/onlinejudge/showProblem.do?problemCode=3659

 #include<cstdio>
 #include<iostream>
 #include<cstring>
 #include<vector>
 #include<algorithm>
 using namespace std;

 const int maxn = ;
 int p[maxn],num[maxn];
 long long int sum[maxn];
 struct Edge{
     int u,v,c;
     bool operator <(const Edge & rh) const{
         return c > rh.c;
     }
 };
 vector<Edge> e;
 int n;

 int find(int x){
     return x == p[x] ? x : p[x] = find(p[x]);
 }
 void init(){
     e.clear();
     memset(sum,,sizeof(sum));
     for(int i=;i<=n;i++){
         p[i] = i;
         num[i] = ;
     }
 }
 int main()
 {
     //if(freopen("input.txt","r",stdin)== NULL)  {printf("Error\n"); exit(0);}

     while(cin>>n){
         init();
         for(int i=;i<n;i++){
             int u,v,c;
             scanf("%d%d%d",&u,&v,&c);
             e.push_back((Edge){u,v,c});
         }
         sort(e.begin(),e.end());
         for(int i=;i<n-;i++){
             int a = find(e[i].u), b = find(e[i].v);
             long long int suma,sumb;
             suma = sum[a] + (long long)num[b]*e[i].c ;
             sumb = sum[b] + (long long)num[a]*e[i].c ;
             if(suma >= sumb) {p[b] = a; sum[a] = suma; num[a] = num[a] + num[b];}
             else             {p[a] = b; sum[b] = sumb; num[b] = num[a] + num[b];}
             //printf("%d %d %d %d\n",a,b,suma,sumb);
         }
         printf("%lld\n",sum[find()]);
     }
 }
 //wa的原因就在于long long没使用正确；
 //本题巧妙的用并查集，归纳递推；