BZOJ2152：聪聪可可

 1 //OJ 2077
 2 //by Cydiater
 3 //2016.9.23
 4 #include <iostream>
 5 #include <cstdio>
 6 #include <cstring>
 7 #include <string>
 8 #include <algorithm>
 9 #include <queue>
10 #include <map>
11 #include <ctime>
12 #include <cmath>
13 #include <iomanip>
14 #include <cstdlib>
15 using namespace std;
16 #define ll long long
17 #define up(i,j,n)        for(int i=j;i<=n;i++)
18 #define down(i,j,n)        for(int i=j;i>=n;i--)
19 const int MAXN=1e6+5;
20 const int oo=0x3f3f3f3f;
21 inline int read(){
22     char ch=getchar();int x=0,f=1;
23     while(ch>‘9‘||ch<‘0‘){if(ch==‘-‘)f=-1;ch=getchar();}
24     while(ch>=‘0‘&&ch<=‘9‘){x=x*10+ch-‘0‘;ch=getchar();}
25     return x*f;
26 }
27 int LINK[MAXN],len=0,sum,max_siz[MAXN],root,siz[MAXN],dis[MAXN],head,tail,q[MAXN],cnt[3],ans=0;
28 bool vis[MAXN];
29 struct edge{
30     int y,next,v;
31 }e[MAXN<<1];
32 int N;
33 namespace solution{
34     inline void insert(int x,int y,int v){e[++len].next=LINK[x];LINK[x]=len;e[len].y=y;e[len].v=v;}
35     inline int gcd(int a,int b){return b==0?a:gcd(b,a%b);}
36     void init(){
37         N=read();
38         memset(vis,0,sizeof(vis));
39         up(i,2,N){
40             int x=read(),y=read(),v=read();
41             insert(x,y,v);
42             insert(y,x,v);
43         }
44     }
45     void make_root(int node,int fa){
46         max_siz[node]=0;siz[node]=1;
47         for(int i=LINK[node];i;i=e[i].next)if(!vis[e[i].y]&&e[i].y!=fa){
48             make_root(e[i].y,node);
49             siz[node]+=siz[e[i].y];
50             max_siz[node]=max(max_siz[node],siz[e[i].y]);
51         }
52         max_siz[node]=max(max_siz[node],sum-max_siz[node]);
53         if(max_siz[node]<max_siz[root])root=node;
54     }
55     void get_deep(int node,int fa){
56         q[++tail]=dis[node];
57         for(int i=LINK[node];i;i=e[i].next)if(e[i].y!=fa&&!vis[e[i].y]){
58             dis[e[i].y]=dis[node]+e[i].v;
59             get_deep(e[i].y,node);
60         }
61     }
62     int col(int node,int dist){
63         dis[node]=dist;head=1;tail=0;
64         get_deep(node,0);
65         cnt[0]=cnt[1]=cnt[2]=0;
66         up(i,head,tail)cnt[q[i]%3]++;
67         return cnt[0]*cnt[0]+2*cnt[1]*cnt[2];
68     }
69     void work(int node){
70         ans+=col(node,0);
71         vis[node]=1;
72         for(int i=LINK[node];i;i=e[i].next)if(!vis[e[i].y]){
73             ans-=col(e[i].y,e[i].v);
74             root=0;
75             make_root(e[i].y,node);
76             work(root);
77         }
78     }
79     void slove(){
80         sum=N;max_siz[0]=oo;root=0;
81         make_root(1,0);
82         work(root);
83     }
84     void output(){
85         int d=gcd(ans,N*N);
86         printf("%d/%d\n",ans/d,N*N/d);
87     }
88 }
89 int main(){
90     //freopen("input.in","r",stdin);
91     using namespace solution;
92     init();
93     slove();
94     output();
95     return 0;
96 }