codevs 1700 MST和树的重心

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#include<iostream>#include<cstdio>#include<cmath>#include<cstring>#include<algorithm>#include<cstdlib>#include<queue>#define fo(i,a,b) for(int i=a;i<=b;i++)#define fod(i,a,b) for(int i=a;i>=b;i--)using namespace std;typedef long long ll;const int MAXN=100000;const int MAXM=200000;const int INF=(1<<30);ll dis[MAXN],mini=-1,re;int n,m,len=0,last[MAXN],fa[MAXN],pre[MAXN];int cur,pos;bool vis[MAXN];struct edge{   int u,v,w;   friend bool operator < (const edge &x,const edge &y){       return x.w<y.w;   }}e[MAXM];int Find(int x){   return x==fa[x]?x:fa[x]=Find(fa[x]);}struct Edge{  int next,to,val;  Edge(int n=0,int v=0,int w=0):next(n),to(v),val(w){}}E[MAXN];void add(int from,int to,int val){E[++len]=Edge(last[from],to,val);last[from]=len;E[++len]=Edge(last[to],from,val);last[to]=len;}void kruskal(){   ll ans=0;    fo(i,1,n) fa[i]=i;   sort(e+1,e+1+m);   fo(i,1,m){     int x=Find(e[i].u),y=Find(e[i].v);     if(x==y) continue;     else{     ans+=e[i].w;     add(e[i].u,e[i].v,e[i].w); fa[x]=y;     }   }   printf("%lld\n",ans);}void dfs(int x){    for(int i=last[x];i;i=E[i].next){   int id=E[i].to;   if(!vis[id]){     pre[id]=x;      dis[id]=dis[x]+E[i].val;      vis[id]=true;      dfs(id);      vis[id]=false;   } }}void search(int x){    if(pre[x]) search(pre[x]);    re=min(re,max(dis[x],mini-dis[x]));}int main(){   memset(vis,0,sizeof(vis));   scanf("%d%d",&n,&m);   fo(i,1,m) {   scanf("%d%d%d",&e[i].u,&e[i].v,&e[i].w);   }   kruskal();      memset(vis,0,sizeof(vis));   memset(dis,0,sizeof(dis));   vis[1]=true;   dfs(1);   fo(i,1,n){   if(dis[i]>mini) mini=dis[cur=i];   }   vis[1]=false;   memset(pre,0,sizeof(pre));   memset(dis,0,sizeof(dis));   vis[cur]=true;   dfs(cur);      mini=-1;   fo(i,1,n){   if(dis[i]>mini) mini=dis[pos=i];   }   re=mini;   search(pos);   printf("%lld",re);   return 0;}
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