洛谷 P3224 [HNOI2012]永无乡

#include<bits/stdc++.h>
#define N 100005
using namespace std;
int n,m,q;
int a[N],pre[N];
int rt[N],lc[N],rc[N],sz[N];
int find(int x)
{
	return x==pre[x] ? x : find(pre[x]);
}
void up(int u)
{
	sz[u]=sz[lc[u]]+sz[rc[u]]+1;
}
void clear(int u)
{
	sz[u]=lc[u]=rc[u]=0;
}
void lrot(int &u)
{
	int t=rc[u];
	rc[u]=lc[t];
	lc[t]=u;
	up(u);
	up(t);
	u=t;
}
void rrot(int &u)
{
	int t=lc[u];
	lc[u]=rc[t];
	rc[t]=u;
	up(u);
	up(t);
	u=t;
}
void mant(int &u)
{
	if(sz[lc[lc[u]]]>sz[rc[u]]) rrot(u);
	if(sz[rc[rc[u]]]>sz[lc[u]]) lrot(u);
}
void ins(int &u,int x)
{
	if(!u) u=x;
	else
	{
		if(a[x]<=a[u]) ins(lc[u],x);
		else ins(rc[u],x);
	}
	sz[u]++;
}
void merg(int u,int v)
{
	if(lc[v]) merg(u,lc[v]);
	if(rc[v]) merg(u,rc[v]);
	clear(v);
	ins(rt[u],v);
	mant(rt[u]);
}
void merge(int x,int y)
{
	x=find(x),y=find(y);
	if(sz[rt[x]]<sz[rt[y]]) swap(x,y);
	if(x!=y) pre[y]=x, merg(x,rt[y]);
}
int sele(int u,int k)
{
	int t=sz[lc[u]]+1;
	if(k<t) return sele(lc[u],k);
	if(k>t) return sele(rc[u],k-t);
	return u;
}
int main()
{
	int x,y;
	char c;
	scanf("%d%d",&n,&m);
	for(int i=1;i<=n;i++)
	{
		scanf("%d",&a[i]);
		pre[i]=i;
		ins(rt[i],i);
	}
	while(m--)
	{
		scanf("%d%d",&x,&y);
		merge(x,y);
	}
	scanf("%d",&q);
	while(q--)
	{
		scanf("\n%c%d%d",&c,&x,&y);
		if(c=='B') merge(x,y);
		else
		{
			x=find(x);
			if(y>sz[rt[x]]) puts("-1");
			else printf("%d\n",sele(rt[x],y));
		}
	}
}