https://www.lydsy.com/JudgeOnline/problem.php?id=2733

https://www.luogu.org/problemnew/show/P3224

C++版本一

题解：线段树+并查集+线段树合并

用并查集维护连通性，每个连通块内建一棵权值线段树，操作只有合并俩线段树以及查询排名

/*
*@Author:   STZG
*@Language: C++
*/
#include <bits/stdc++.h>
#include<iostream>
#include<algorithm>
#include<cstdlib>
#include<cstring>
#include<cstdio>
#include<string>
#include<vector>
#include<bitset>
#include<queue>
#include<deque>
#include<stack>
#include<cmath>
#include<list>
#include<map>
#include<set>
//#define DEBUG
#define RI register int
#define endl "\n"
using namespace std;
typedef long long ll;
//typedef __int128 lll;
const int N=100000+10;
const int M=2000000+10;
const int MOD=1e9+7;
const double PI = acos(-1.0);
const double EXP = 1E-8;
const int INF = 0x3f3f3f3f;
int t,n,m,k,p,l,r,q,sz;
int ans,cnt,flag,temp;
int v[N],id[N],fa[N],root[N];
int ls[M],rs[M],sum[M];
int find(int x){
	return x==fa[x]?x:fa[x]=find(fa[x]);
}
void insert(int &k,int l,int r,int val){
	if(!k)k=++sz;
	if(l==r){
		sum[k]=1;return;
	}
	int mid=(l+r)>>1;
	if(val<=mid)insert(ls[k],l,mid,val);
	else insert(rs[k],mid+1,r,val);
	sum[k]=sum[ls[k]]+sum[rs[k]];
}
int query(int k,int l,int r,int rank){
	if(l==r)return l;
	int mid=(l+r)>>1;
	if(sum[ls[k]]>=rank)return query(ls[k],l,mid,rank);
	else return query(rs[k],mid+1,r,rank-sum[ls[k]]);
}
int merge(int x,int y){
	if(!x)return y;
	if(!y)return x;
	ls[x]=merge(ls[x],ls[y]);
	rs[x]=merge(rs[x],rs[y]);
	sum[x]=sum[ls[x]]+sum[rs[x]];
	return x;
}
int main()
{
#ifdef DEBUG
	freopen("input.in", "r", stdin);
	//freopen("output.out", "w", stdout);
#endif
    //ios::sync_with_stdio(false);
    //cin.tie(0);
    //cout.tie(0);
    //scanf("%d",&t);
    //while(t--){
    scanf("%d%d",&n,&m);
    for(int i=1;i<=n;i++){
        scanf("%d",&v[i]);
    }
	for(int i=1;i<=n;i++)fa[i]=i;
	int x,y;
	for(int i=1;i<=m;i++){
        scanf("%d%d",&x,&y);
		int tx=find(x);
        int ty=find(y);
	    fa[tx]=ty;
	}
	for(int i=1;i<=n;i++){
		insert(root[find(i)],1,n,v[i]);
		id[v[i]]=i;
	}
    scanf("%d",&q);char ch[2];
	while(q--){
		scanf("%s",ch);
		scanf("%d%d",&x,&y);
		if(ch[0]=='Q'){
			int p=find(x);
			if(sum[root[p]]<y){
				puts("-1");continue;
			}
			int t=query(root[p],1,n,y);
		    printf("%d\n",id[t]);
		}else {
			int p=find(x),q=find(y);
			if(p!=q){
				fa[p]=q;
				root[q]=merge(root[p],root[q]);
			}
		}
	}
    //}

#ifdef DEBUG
	printf("Time cost : %lf s\n",(double)clock()/CLOCKS_PER_SEC);
#endif
    //cout << "Hello world!" << endl;
    return 0;
}

C++版本二

题解：平衡树