Chairman of the trees still small section of the template k - structure

#include<cstdio>
#include<cstring>
#include<cstdlib>
#include<algorithm>

using namespace std;

const int maxn = 2e5 + 10;

struct node
{
    int l, r, sum;
};

node tree[maxn * 40];
int tot;
int rt[maxn], a[maxn], b[maxn];

int build(int l, int r)
{
    int rt = ++tot;
    tree[rt].sum = 0;
    if(l == r)
    {
        return rt;
    }
    int mid = (l + r)>>1;
    tree[rt].l = build(l, mid);
    tree[rt].r = build(mid + 1, r);
    return rt;
}

int update(int pre, int l, int r, int p)
{
    int rt = ++ tot;
    tree[rt].l = tree[pre].l;
    tree[rt].r = tree[pre].r;
    tree[rt].sum = tree[pre].sum + 1;
   // printf("sss %d %d %d\n", l, r, tree[rt].sum);
    if(l == r)
    {
        return rt;
    }
    int mid = (l + r)>>1;
   // printf("%d %d\n", mid, p);
    if(p <= mid) tree[rt].l = update(tree[rt].l, l, mid, p);
    else tree[rt].r = update(tree[rt].r, mid + 1, r, p);
    return rt;
}

int query(int fro, int now,int l, int r, int k)
{
    //printf("sss%d %d\n", l, r);
    if(l == r) return l;
    int mid = (l + r)>>1;
    int x = tree[tree[now].l].sum - tree[tree[fro].l].sum;
    //printf("%d %d\n", x, k);
    if(x >= k) return query(tree[fro].l, tree[now].l, l, mid, k);
    else return query(tree[fro].r, tree[now].r, mid + 1, r, k - x);
}

int main()
{
    int n, q;
    tot = 0;
    scanf("%d%d", &n, &q);
    for(int i = 1; i <= n; i++)
    {
        scanf("%d", &a[i]);
        b[i] = a[i];
    }
    sort(b + 1, b + n + 1);
    int m = unique(b + 1, b + n + 1) - b - 1;
    rt[0] = build(1, m);
    for(int i = 1; i <= n; i++)
    {
        int pos = lower_bound(b + 1, b + 1 + m, a[i]) - b;
        //printf("%d\n", pos);
        rt[i] = update(rt[i - 1], 1, m, pos);
    }
    while(q--)
    {
        int l, r, k;
        scanf("%d%d%d", &l, &r, &k);
        int ans = query(rt[l - 1], rt[r], 1,  m, k);
        //printf("%d\n", ans);
        printf("%d\n", b[ans]);
    }
    return 0;
}