树型DP。
#include<iostream> #include<cstdio> #include<cstring> #include<algorithm> #define maxv 200500 #define maxe 300500 #define inf 1000000007 using namespace std; long long n,x,y,z,c[maxv],nume=0,g[maxv],val[maxv],sum=0,ans,dis[maxv]; struct edge { long long v,w,nxt; }e[maxe]; void addedge(long long u,long long v,long long w) { e[++nume].v=v; e[nume].w=w; e[nume].nxt=g[u]; g[u]=nume; } void dfs1(long long x,long long fath) { val[x]=c[x]; for (long long i=g[x];i;i=e[i].nxt) { long long v=e[i].v; if (v!=fath) { dis[v]=dis[x]+e[i].w; dfs1(v,x); val[x]+=val[v]; } } } void dfs2(long long x,long long fath,long long now) { for (long long i=g[x];i;i=e[i].nxt) { long long v=e[i].v; if (v!=fath) { long long re=now-val[v]*e[i].w+(sum-val[v])*e[i].w; ans=min(ans,re); dfs2(v,x,re); } } } int main() { scanf("%lld",&n); for (long long i=1;i<=n;i++) { scanf("%lld",&c[i]); sum+=c[i]; } for (long long i=1;i<=n-1;i++) { scanf("%lld%lld%lld",&x,&y,&z); addedge(x,y,z); addedge(y,x,z); } dfs1(1,1); for (long long i=1;i<=n;i++) ans+=c[i]*dis[i]; dfs2(1,1,ans); printf("%lld\n",ans); return 0; }
时间: 2024-11-03 10:18:25