BZOJ1827: [Usaco2010 Mar]gather 奶牛大集会

  1 #include<cstdio>
  2 
  3 #include<cstdlib>
  4 
  5 #include<cmath>
  6 
  7 #include<cstring>
  8 
  9 #include<algorithm>
 10 
 11 #include<iostream>
 12 
 13 #include<vector>
 14 
 15 #include<map>
 16 
 17 #include<set>
 18 
 19 #include<queue>
 20 
 21 #include<string>
 22 
 23 #define inf 100000000000000
 24 
 25 #define maxn 150000
 26 
 27 #define maxm 500+100
 28 
 29 #define eps 1e-10
 30 
 31 #define ll long long
 32 
 33 #define pa pair<int,int>
 34 
 35 #define for0(i,n) for(int i=0;i<=(n);i++)
 36 
 37 #define for1(i,n) for(int i=1;i<=(n);i++)
 38 
 39 #define for2(i,x,y) for(int i=(x);i<=(y);i++)
 40 
 41 #define for3(i,x,y) for(int i=(x);i>=(y);i--)
 42 
 43 #define mod 1000000007
 44 
 45 using namespace std;
 46 
 47 inline int read()
 48 
 49 {
 50 
 51     int x=0,f=1;char ch=getchar();
 52 
 53     while(ch<‘0‘||ch>‘9‘){if(ch==‘-‘)f=-1;ch=getchar();}
 54 
 55     while(ch>=‘0‘&&ch<=‘9‘){x=10*x+ch-‘0‘;ch=getchar();}
 56 
 57     return x*f;
 58 
 59 }
 60 struct edge{int go,next;ll w;}e[2*maxn];
 61 int n,tot,head[maxn];
 62 ll sum,s[maxn],f[maxn];
 63 bool v[maxn];
 64 inline void insert(int x,int y,int z)
 65 {
 66     e[++tot].go=y;e[tot].next=head[x];head[x]=tot;e[tot].w=z;
 67     e[++tot].go=x;e[tot].next=head[y];head[y]=tot;e[tot].w=z;
 68 }
 69 void dfs(int x)
 70 {
 71     v[x]=1;
 72     for(int i=head[x],y;i;i=e[i].next)
 73     if(!v[y=e[i].go])
 74     {
 75         dfs(y);
 76         s[x]+=s[y];
 77         f[x]+=f[y]+s[y]*e[i].w;
 78     }
 79 }
 80 void dp(int x)
 81 {
 82     v[x]=0;
 83     for(int i=head[x],y;i;i=e[i].next)
 84     if(v[y=e[i].go])
 85     {
 86         f[y]=f[x]+(sum-s[y]-s[y])*e[i].w;
 87         dp(y);
 88     }
 89 }
 90 
 91 int main()
 92 
 93 {
 94 
 95     freopen("input.txt","r",stdin);
 96 
 97     freopen("output.txt","w",stdout);
 98 
 99     n=read();
100     for1(i,n)s[i]=read(),sum+=s[i];
101     for1(i,n-1){int x=read(),y=read(),z=read();insert(x,y,z);}
102     dfs(1);
103     dp(1);
104     ll ans=inf;
105     for1(i,n)ans=min(ans,f[i]);
106     printf("%lld\n",ans);
107 
108     return 0;
109 
110 }