3306: 树 树上倍增

傻逼题，换根分三种情况讨论。

#include<iostream>
#include<cstdio>
using namespace std;
const int inf=1000000007;
const int N=100005;
int head[N],next[N],list[N],in[N],out[N],deep[N],pos[N],val[N],fa[N][18];
int n,Q,root,cnt,dfn;
int l[N<<2],r[N<<2],mn[N<<2];
inline int read()
{
    int a=0,f=1; char c=getchar();
    while (c<'0'||c>'9') {if (c=='-') f=-1; c=getchar();}
    while (c>='0'&&c<='9') {a=a*10+c-'0'; c=getchar();}
    return a*f; 
}
inline void insert(int x,int y)
{
    next[++cnt]=head[x];
    head[x]=cnt;
    list[cnt]=y;
}
void dfs(int x)
{
    in[x]=++dfn; pos[dfn]=x;
    for (int i=1;(1<<i)<=deep[x];i++)
        fa[x][i]=fa[fa[x][i-1]][i-1];
    for (int i=head[x];i;i=next[i])
    {
        deep[list[i]]=deep[x]+1;
        fa[list[i]][0]=x;
        dfs(list[i]);
    }
    out[x]=dfn;
}
inline int lca(int x,int y)
{
    if (deep[x]<deep[y]) swap(x,y);
    int t=deep[x]-deep[y];
    for (int i=17;~i;i--)
        if ((1<<i)&t) x=fa[x][i];
    for (int i=0;i<=17;i++)
        if (fa[x][i]!=fa[y][i])
            x=fa[x][i],y=fa[y][i];
    return x==y?x:fa[x][0];
}
inline void pushup(int k)
{
    mn[k]=min(mn[k<<1],mn[k<<1|1]);
}
void build(int k,int x,int y)
{
    l[k]=x; r[k]=y;
    if (l[k]==r[k]) 
    {
        mn[k]=val[pos[l[k]]];
        return;
    }
    int mid=l[k]+r[k]>>1;
    build(k<<1,x,mid); build(k<<1|1,mid+1,y);
    pushup(k);
}
void modify(int k,int x,int y)
{
    if (l[k]==r[k]) 
    {
        mn[k]=y;
        return;
    }
    int mid=l[k]+r[k]>>1;
    if (x<=mid) modify(k<<1,x,y);
    else modify(k<<1|1,x,y);
    pushup(k);
}
int query(int k,int x,int y)
{
    if (x>y) return inf;
    if (l[k]==x&&r[k]==y) return mn[k];
    int mid=l[k]+r[k]>>1;
    if (y<=mid) return query(k<<1,x,y);
    else if (x>mid) return query(k<<1|1,x,y);
    else return min(query(k<<1,x,mid),query(k<<1|1,mid+1,y));
}
inline int find(int x,int f)
{
    int y=x;
    for (int i=17;~i;i--)
        if (deep[fa[y][i]]>deep[f])
            y=fa[y][i];
    return y;
}
int main()
{
    n=read(); Q=read();
    for (int i=1;i<=n;i++)
    {
        int f=read();
        val[i]=read();
        if (!f) root=i;
        else insert(f,i);       
    }
    dfs(1);
    build(1,1,n);
    while (Q--)
    {
        char opt[5];
        scanf("%s",opt);
        int x=read(),y;
        switch (opt[0])
        {
            case 'V':
                y=read();
                modify(1,in[x],y);
                break;
            case 'E':
                root=x;
                break;
            case 'Q':
                if (root==x) printf("%d\n",mn[1]);
                else
                {
                    int t=lca(x,root);
                    if (t!=x) printf("%d\n",query(1,in[x],out[x]));
                    else
                    {
                        int u=find(root,x);
                        printf("%d\n",min(query(1,1,in[u]-1),query(1,out[u]+1,n)));
                    }
                }
                break;
        }
    }
    return 0;
}