【题解】 bzoj2435: [Noi2011]道路修建 （傻逼题）

bzoj2435，懒得复制，戳我戳我

Solution:

• 模拟即可（有点傻逼啊

Code:

//It is coded by Ning_Mew on 5.13
#include<bits/stdc++.h>
#define LL long long
using namespace std;

const int maxn=1e6+7;

int n;
LL ans=0;
int siz[maxn];
int head[maxn],cnt=0;
struct Edge{
  int nxt,to,dis;
}edge[maxn*2];

void add(int from,int to,int dis){
  edge[++cnt].nxt=head[from];edge[cnt].to=to;
  edge[cnt].dis=dis;head[from]=cnt;
}
void dfs(int fa,int u){
  siz[u]=1;
  for(int i=head[u];i!=0;i=edge[i].nxt){
    int v=edge[i].to;if(v==fa)continue;
    dfs(u,v);
    siz[u]+=siz[v];
    ans+=abs(n-siz[v]-siz[v])*edge[i].dis;
  }return;
}
int main(){
  scanf("%d",&n);
  for(int i=1;i<n;i++){
    int x,y,z;scanf("%d%d%d",&x,&y,&z);
    add(x,y,z);add(y,x,z);
  }
  dfs(1,1);
  printf("%lld\n",ans);
  return 0;
}