mirror of
https://github.com/Kiritow/OJ-Problems-Source.git
synced 2024-03-22 13:11:29 +08:00
60 lines
1.2 KiB
C++
60 lines
1.2 KiB
C++
#include <iostream>
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#include <string.h>
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#include <stdio.h>
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using namespace std;
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#define N 10010
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struct note
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{
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int v,next,value;
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}edge[N*2+10];
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int head[N];
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double dp[N];
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int sum[N];
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int n;
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int kk;
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int ss;
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void add(int fa,int son,int value)
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{
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edge[kk].v = son;
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edge[kk].value = value;
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edge[kk].next = head[fa];
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head[fa] = kk++;
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}
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void dfs(int root,int fa)
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{
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sum[root] = 1;
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for(int i = head[root];i != -1;i = edge[i].next)
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{
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int son = edge[i].v;
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if(son == fa) continue;
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dfs(son,root);
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sum[root] += sum[son];
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ss += sum[son]*(n-sum[son]);
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dp[root] += dp[son] + (double)sum[son]*(n-sum[son])*edge[i].value;
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}
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}
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int main()
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{
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int cas;
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scanf("%d",&cas);
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while(cas--)
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{
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ss = 0;
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memset(head,-1,sizeof(head));
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memset(dp,0,sizeof(dp));
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kk = 1;
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scanf("%d",&n);
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int a,b,v;
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for(int i = 1;i < n;i++)
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{
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scanf("%d%d%d",&a,&b,&v);
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add(a,b,v);
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add(b,a,v);
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}
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dfs(0,-1);
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ss = n*(n-1) / 2;
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printf("%llf\n",(double)dp[0] / ss);
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}
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return 0;
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}
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