【BZOJ】1036 [ZJOI2008]树的统计Count

【算法】树链剖分+线段树

【题解】模板题，见http://www.cnblogs.com/onioncyc/p/6207462.html

调用线段数时要用新编号pos[i] ！！！

#include<cstdio>
#include<cctype>
#include<algorithm>
using namespace std;
const int maxn=30010,inf=0x3f3f3f3f;
int pos[maxn],top[maxn],dfsnum,f[maxn],deep[maxn],size[maxn],first[maxn],n,tot,a[maxn];
struct edge{int u,v,from;}e[maxn*3];
struct tree{int l,r,sum,mx;}t[maxn*3]; 
int read()
{
    char c;int s=0,t=1;
    while(!isdigit(c=getchar()))if(c=='-')t=-1;
    do{s=s*10+c-'0';}while(isdigit(c=getchar()));
    return s*t;
}
void insert(int u,int v)
{tot++;e[tot].u=u;e[tot].v=v;e[tot].from=first[u];first[u]=tot;}
void dfs1(int x,int fa)
{
    size[x]=1;
    for(int i=first[x];i;i=e[i].from)
     if(e[i].v!=fa)
      {
          int y=e[i].v;
          deep[y]=deep[x]+1;
          f[y]=x;
          dfs1(y,x);
          size[x]+=size[y];
      }
}
void dfs2(int x,int tp,int fa)
{
    int k=0;
    pos[x]=++dfsnum;
    top[x]=tp;
    for(int i=first[x];i;i=e[i].from)
     if(e[i].v!=fa&&size[e[i].v]>size[k])k=e[i].v;
    if(k==0)return;
    dfs2(k,tp,x);
    for(int i=first[x];i;i=e[i].from)
     if(e[i].v!=fa&&e[i].v!=k)dfs2(e[i].v,e[i].v,x);
}
void build(int k,int l,int r)
{
    t[k].l=l;t[k].r=r;
    if(l!=r)
     {
         int mid=(l+r)>>1;
         build(k<<1,l,mid);
         build(k<<1|1,mid+1,r);
     }
}
void change(int k,int x,int y)
{
    int left=t[k].l,right=t[k].r;
    if(left==right){t[k].mx=y;t[k].sum=y;}
     else
      {
          int mid=(left+right)>>1;
          if(x<=mid)change(k<<1,x,y);
           else change(k<<1|1,x,y);
          t[k].sum=t[k<<1].sum+t[k<<1|1].sum;
          t[k].mx=max(t[k<<1].mx,t[k<<1|1].mx);
      }
}
int ask_mx(int k,int l,int r)
{
    int left=t[k].l,right=t[k].r;
    if(l<=left&&right<=r)return t[k].mx;
     else
      {
          int mid=(left+right)>>1,maxs=-inf;
          if(l<=mid)maxs=ask_mx(k<<1,l,r);
          if(r>mid)maxs=max(maxs,ask_mx(k<<1|1,l,r));
          return maxs;
      }
}
int ask_sum(int k,int l,int r)
{
    int left=t[k].l,right=t[k].r;
    if(l<=left&&right<=r)return t[k].sum;
     else
      {
          int mid=(left+right)>>1,sums=0;
          if(l<=mid)sums=ask_sum(k<<1,l,r);
          if(r>mid)sums+=ask_sum(k<<1|1,l,r);
          return sums;
      }
}
int solve_mx(int x,int y)
{
    int maxs=-inf;
    while(top[x]!=top[y])
     {
         if(deep[top[x]]<deep[top[y]])swap(x,y);
         maxs=max(maxs,ask_mx(1,pos[top[x]],pos[x]));
         x=f[top[x]];
     }
    if(pos[x]>pos[y])swap(x,y);
    maxs=max(maxs,ask_mx(1,pos[x],pos[y]));
    return maxs;
}
int solve_sum(int x,int y)
{
    int sums=0;
    while(top[x]!=top[y])
     {
         if(deep[top[x]]<deep[top[y]])swap(x,y);
         sums+=ask_sum(1,pos[top[x]],pos[x]);
         x=f[top[x]];
     }
    if(pos[x]>pos[y])swap(x,y);
    sums+=ask_sum(1,pos[x],pos[y]);
    return sums;
}
int main()
{
    n=read();
    for(int i=1;i<n;i++)
     {
         int u=read(),v=read();
         insert(u,v);
         insert(v,u);
     }
    for(int i=1;i<=n;i++)a[i]=read();
    dfs1(1,-1);
    dfs2(1,1,-1);
    build(1,1,n);
    for(int i=1;i<=n;i++)change(1,pos[i],a[i]);
    int Q=read();char ch[10];
    for(int i=1;i<=Q;i++)
     {
         scanf("%s",ch);
         int u=read(),v=read();
         if(ch[1]=='H')change(1,pos[u],v);//QAQ 调用线段树必须用新编号，下面用旧编号是因为子程序中用了新编号T_T 
         if(ch[1]=='M')printf("%d\n",solve_mx(u,v));
         if(ch[1]=='S')printf("%d\n",solve_sum(u,v));
     }
    return 0;
}