Chairman Tree Template

Reference Wuyiqi

#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;
const int maxn = 100010;
int ls[maxn*20], rs[maxn*20], sum[maxn*20];
int T[maxn], tot;

void build(int l, int r, int& rt)
{
	rt = ++tot;
	sum[rt] = 0;
	if(l == r)
		return;
	int m = l+r>>1;
	build(l, m, ls[rt]);
	build(m+1, r, rs[rt]);
}

void update(int last, int p, int l, int r, int& rt)
{
	rt = ++tot;
	ls[rt] = ls[last];
	rs[rt] = rs[last];
	sum[rt] = sum[last]+1;
	if(l == r)
		return;
	int m = l+r>>1;
	if(p <= m)
		update(ls[last], p, l, m, ls[rt]);
	else
		update(rs[last], p, m+1, r, rs[rt]);
}

int query(int x, int y, int l, int r, int k)
{
	if(l == r)
		return l;
	int m = l+r>>1;
	int cnt = sum[ls[y]]-sum[ls[x]];
	if(k <= cnt)
		return query(ls[x], ls[y], l, m, k);
	else
		return query(rs[x], rs[y], m+1, r, k-cnt);
}
int num[maxn], a[maxn], n, q;
void cal()
{
	for(int i = 1; i <= n; i++)
	{
		scanf("%d", &a[i]);
		num[i] = a[i];
	}
	tot = 0;
	sort(num+1, num+n+1);
	int cnt = unique(num+1, num+n+1)-(num+1);
	build(1, cnt, T[0]);
	for(int i = 1; i <= n; i++)
	{
		a[i] = lower_bound(num+1, num+cnt+1, a[i])-num;
	}
	for(int i = 1; i <= n; i++)
		update(T[i-1], a[i], 1, cnt, T[i]);
	while(q--)
	{
		int x, y, k;
		scanf("%d %d %d", &x, &y, &k);
		printf("%d\n", num[query(T[x-1], T[y], 1, cnt, k)]);
	}
}
int main()
{
	int T;
	scanf("%d", &T);
	while(T--)
	{
		scanf("%d %d", &n, &q);
		cal();
	}
	return 0;
}