[poj2104]kth-number(归并树求区间第k大)

复杂度：$O(nlog^3n)$

#include<cstdio>
#include<cstring>
#include<algorithm>
#include<cstdlib>
#include<iostream>
#include<cmath>
#define MAXN 100000
using namespace std;
int sorted[][MAXN],a[MAXN];
void build(int deep,int l,int r){
    if(l==r){
        sorted[deep][l]=a[l];
        return;
    }
    int mid=(l+r)>>;
    build(deep+,l,mid);
    build(deep+,mid+,r);
    int p=l,q=mid+,k=l;
    while(p<=mid&&q<=r){
        if(sorted[deep+][p]<=sorted[deep+][q])
            sorted[deep][k++]=sorted[deep+][p++];
        else sorted[deep][k++]=sorted[deep+][q++];
    }
    while(p<=mid) sorted[deep][k++]=sorted[deep+][p++];
    while(q<=r) sorted[deep][k++]=sorted[deep+][q++];//存储序列
}
//查询某个数在区间内的rank
int query(int deep,int l,int r,int tl,int tr,int k){
    if(tr<l||tl>r) return ;
    if(tl<=l&&r<=tr)
        return lower_bound(&sorted[deep][l],&sorted[deep][r]+,k)-&sorted[deep][l];
    int mid=(l+r)>>;
    return query(deep+,l,mid,tl,tr,k)+query(deep+,mid+,r,tl,tr,k);
}

int solve(int n,int tl, int tr, int k){
    int l=,r=n;
    while(l<r){
        int mid=(l+r+)>>;
        int cnt=query(,,n,tl,tr,sorted[][mid]);
        if(cnt<=k) l=mid;
        else r=mid-;
    }
    return sorted[][l];
}

int main(){
    int n,m;
    scanf("%d%d", &n, &m);
    for(int i=;i<=n;i++) scanf("%d",&a[i]);
    build(,,n);
    while(m--){
        int tl,tr,k;
        scanf("%d%d%d", &tl, &tr, &k);
        printf("%d\n", solve(n,tl,tr,k-));
    }
    return ;
}