QTREEⅠ SPOJ

树剖模板，注意把边化为点后要查到y的儿子。

 #include<bits/stdc++.h>
 using namespace std;
 const int N=;
 int f[N],bel[N],w[N],id[N],pos[N],d[N],size[N],son[N],head[N];
 int n,idx,cnt,num,T,rt;
 struct node
 {
     int l,r,s,mx;
     void clean()
     {
         l=r=s=mx=-1e9;
     }
 }t[N<<];
 struct edge
 {
     int to,nex,w,x;
 }e[N<<],a[N];
 void add(int x,int y,int w)
 {
     e[++cnt].to=y;e[cnt].nex=head[x];head[x]=cnt;e[cnt].x=x;
 }
 void dfs1(int x,int fa)
 {
     size[x]=;
     for(int i=head[x];i;i=e[i].nex)
     {
         int y=e[i].to;
         if(y==fa)continue;
         f[y]=x;d[y]=d[x]+;
         dfs1(y,x);
         if(size[y]>size[son[x]])son[x]=y;
         size[x]+=size[y];
     }
     return;
 }
 void dfs2(int x,int chain)
 {
     bel[x]=chain;pos[x]=++idx;id[idx]=x;
     if(son[x])dfs2(son[x],chain);
     for(int i=head[x];i;i=e[i].nex)
     {
         int y=e[i].to;
         if(y==f[x]||y==son[x])continue;
         dfs2(y,y);
     }
 }
 void build(int &x,int l,int r)
 {
     x=++num;
     if(l==r){
         t[x].s=t[x].mx=w[l];return;
     }
     int mid=l+r>>;
     build(t[x].l,l,mid);build(t[x].r,mid+,r);
     t[x].mx=max(t[t[x].l].mx,t[t[x].r].mx);
     return;
 }
 int query(int x,int l,int r,int L,int R)
 {
     if(l==L&&r==R)return t[x].mx;
     int mid=l+r>>;
     if(R<=mid)return query(t[x].l,l,mid,L,R);
     else if(L>mid)return query(t[x].r,mid+,r,L,R);
     else return max(query(t[x].l,l,mid,L,mid),query(t[x].r,mid+,r,mid+,R));
 }
 void change(int x,int l,int r,int pos,int ww)
 {
     if(l==r){t[x].s=t[x].mx=ww;return;}
     int mid=l+r>>;
     if(pos<=mid)change(t[x].l,l,mid,pos,ww);
     else change(t[x].r,mid+,r,pos,ww);
     t[x].mx=max(t[t[x].l].mx,t[t[x].r].mx);
 }
 int querytree(int x,int y)
 {
     int ans=-1e9;
     while(bel[x]!=bel[y])
     {
         if(d[bel[x]]<d[bel[y]])swap(x,y);
         ans=max(ans,query(rt,,n,pos[bel[x]],pos[x]));
         x=f[bel[x]];
     }
     if(d[x]<d[y])swap(x,y);
     if(d[son[y]]<=d[x])
     ans=max(ans,query(rt,,n,pos[son[y]],pos[x]));
     return ans;
 }
 void init()
 {
     memset(f,,sizeof(f));
     memset(d,,sizeof(d));
     memset(size,,sizeof(size));
     memset(son,,sizeof(son));
     memset(bel,,sizeof(bel));
     memset(pos,,sizeof(pos));
     memset(head,,sizeof(head));
     memset(id,,sizeof(id));
     memset(w,,sizeof(w));cnt=idx=num=;rt=;
     for(int i=;i<=num;++i)t[i].clean();
 }
 int main()
 {
     scanf("%d",&T);
     while(T--)
     {
         init();int x,y,ww;
         scanf("%d",&n);
         for(int i=;i<n;++i)
         {
             scanf("%d%d%d",&x,&y,&ww);
             add(x,y,ww);add(y,x,ww);
             a[i].x=x;a[i].to=y;a[i].w=ww;
         }
         dfs1(,);dfs2(,);
         build(rt,,n);char s[];
         for(int i=;i<n;i++)
         {
             x=d[a[i].x]>d[a[i].to]?a[i].x:a[i].to;
             change(rt,,n,pos[x],a[i].w);
         }
         change(rt,,n,pos[],-1e9);
         while()
         {
             scanf("%s",s);
             if(s[]=='D')break;
             if(s[]=='Q')
             {
                 scanf("%d%d",&x,&y);
                 printf("%d\n",querytree(x,y));
             }
             else
             {
                 scanf("%d%d",&x,&y);
                 x=d[a[x].x]>d[a[x].to]?a[x].x:a[x].to;
                 change(rt,,n,pos[x],y);
             }
         }
     }
     return ;
 }