POJ 2104 K-th Number 主席树

#include <iostream>
#include <cstdio>
#include <cmath>
#include <cstring>
#include <algorithm>
using namespace std;
const int N = 1e5+10, M = 1e5, mod = 1e9, inf = 1e9+9;
typedef long long ll;

int n,q,a[N],pos[N],c[N];
struct cooltree{
    struct node {int l,r,v;}tr[N*20];
    int sz,root[N];
    void init() {
        sz = 0, root[0] = 0;
    }
    void update(int &k,int l,int r,int x) {
        tr[++sz] = tr[k], k = sz;
        ++tr[k].v;
        if(l==r) return ;
        int mid = (l+r)>>1;
        if(x <= mid) update(tr[k].l,l,mid,x);
        else update(tr[k].r,mid+1,r,x);
    }
    int ask(int x,int y,int k) {
        int l = 1, r = n;
        x = root[x-1], y = root[y];
        while(l!=r) {
            int mid = (l+r)>>1, now = tr[tr[y].l].v - tr[tr[x].l].v;
            if(k <= now) x = tr[x].l,y = tr[y].l, r = mid;
            else x =tr[x].r , y = tr[y].r, l = mid + 1, k-=now;
        }
        return a[l];
    }
}T;
int main() {
    T.init();
    scanf("%d%d",&n,&q);
    for(int i=1;i<=n;i++) scanf("%d",&a[i]), c[i] = a[i];
    sort(a+1,a+n+1);
    int cnt = unique(a+1,a+n+1) - a - 1;
    //cout<<cnt<<endl;
    for(int i=1;i<=n;i++) pos[i] = lower_bound(a+1,a+cnt+1,c[i]) - a;
    for(int i=1;i<=n;i++) T.update(T.root[i] = T.root[i-1],1,n,pos[i]);
    for(int i=1;i<=q;i++) {
            int x,y,z;
        scanf("%d%d%d",&x,&y,&z);
        printf("%d\n",T.ask(x,y,z));
    }
    return 0;
}