1737 配对

 1 #include <cstdio>
 2 #include <cctype>
 3 #include <vector>
 4 
 5 typedef long long LL;
 6 const int MAXN=100010;
 7 
 8 int n;
 9 
10 LL ans;
11 
12 int son[MAXN];
13 
14 struct node {
15     int to,val;
16     node() {}
17     node(int to,int val):to(to),val(val) {}
18 };
19 
20 std::vector<node> Graph[MAXN];
21 
22 inline void read(int&x) {
23     int f=1;register char c=getchar();
24     for(x=0;!isdigit(c);c==‘-‘&&(f=-1),c=getchar());
25     for(;isdigit(c);x=x*10+c-48,c=getchar());
26     x=x*f;
27 }
28 
29 void DFS(int now,int fa) {
30     son[now]=1;
31     for(register int i=0;i<Graph[now].size();++i) {
32         node p=Graph[now][i];
33         if(p.to==fa) continue;
34         DFS(p.to,now);
35         son[now]+=son[p.to];
36     }
37     return;
38 }
39 
40 void DFS_Ans(int now,int fa) {
41     for(register int i=0;i<Graph[now].size();++i) {
42         node p=Graph[now][i];
43         if(p.to==fa) continue;
44         DFS_Ans(p.to,now);
45         ans+=(LL)(son[p.to]<n-son[p.to]?son[p.to]:(n-son[p.to]))*p.val;
46     }
47     return;
48 }
49 
50 int hh() {
51     read(n);
52     for(register int x,y,z,i=1;i<n;++i) {
53         read(x);read(y);read(z);
54         Graph[y].push_back(node(x,z));
55         Graph[x].push_back(node(y,z));
56     }
57     DFS(1,0);
58     DFS_Ans(1,0);
59     printf("%lld\n",ans);
60     return 0;
61 }
62 
63 int sb=hh();
64 int main(int argc,char**argv) {;}