#include <stdio.h>
#include <math.h>
#include <set>
#include <algorithm>
#define Maxn 1000005
#define Maxm 1000005
int n,m,blg[Maxn],a[Maxn],b[Maxn],bs[Maxn],cnt[Maxn],len,ans[Maxn],cn,ls,c;
struct lxl {
	int id,l,r,k;
    bool operator < (const lxl a) const{
        return blg[l] == blg[a.l] ? (r < a.r) : (blg[l] < blg[a.l]);
    }
} q[Maxm];
struct node{
    int id,val;
    bool operator < (const node &a) const{
        return val < a.val;
    }
};
inline int read() {
    int res = 0,ch = getchar();
    while(ch < '0' || ch > '9') ch = getchar();
    while(ch >= '0' && ch <= '9') res = (res << 3) + (res << 1) + (ch - '0') , ch = getchar();
    return res;
}
inline void add(int x){
	if(!cnt[x]) c++;
    b[cnt[x]]--;
    bs[blg[cnt[x]]]--;
    b[++cnt[x]]++;
    bs[blg[cnt[x]]]++;  
}
inline void del(int x){
    b[cnt[x]]--;
    bs[blg[cnt[x]]]--;
    b[--cnt[x]]++;
    bs[blg[cnt[x]]]++;
    if(!cnt[x]) c--;
}
inline int find(int k)
{
	if(k > c) return -1;
    int f = 1,p;
    while(k > bs[f]) k -= bs[f],f++;
    p = (f - 1) * len + 1;
    while(k > b[p]) k -= b[p],p++;
    return p;
}
std::multiset <node> s;
int main() {
    n = read(),m = read();
    len = (int) sqrt(n);
    for(int i = 1 ; i <= n ; i++) blg[i] = (i - 1) / n + 1 , s.insert({i , read()});
    for(std::multiset<node>::iterator it = s.begin() ; it != s.end() ; ls = it->val,it++) a[it->id] = it->val == ls ? cn : ++cn;
    for(int i = 1 ; i <= m ; i++) q[i] = {i , read() , read() , read()};                                                       
    std::sort(q + 1, q + m + 1);
    int l = 1,r = 0;
    for(int i = 1 ; i <= m ; i++) 
    {
        while(l > q[i].l) add(a[--l]);
        while(r < q[i].r) add(a[++r]);
        while(l < q[i].l) del(a[l++]);
        while(r > q[i].r) del(a[r--]);
        ans[q[i].id] = find(q[i].k);
    }
    for(int i = 1 ; i <= m ; i++) printf("%d\n",ans[i]);
    return 0;
}

我觉得复杂度是没问题的，为什么 7 个点全部 TLE 了