POJ2104：K-th Number——题解

#include<cstdio>
#include<queue>
#include<cctype>
#include<cstring>
#include<cmath>
#include<vector>
#include<algorithm>
using namespace std;
const int N=100001;
inline int read(){
    int X=0,w=0;char ch=0;
    while(!isdigit(ch)){w|=ch==‘-‘;ch=getchar();}
    while(isdigit(ch))X=(X<<3)+(X<<1)+(ch^48),ch=getchar();
    return w?-X:X;
}
struct tree{
    int l;
    int r;
    int sum;
}tr[N*20];
int a[N],b[N],rt[N],n,m,q,pool;
inline void insert(int &y,int &x,int l,int r,int p){
    tr[x=++pool]=tr[y];
    tr[x].sum++;
    if(l==r)return;
    int mid=(l+r)>>1;
    if(p<=mid)insert(tr[y].l,tr[x].l,l,mid,p);
    else insert(tr[y].r,tr[x].r,mid+1,r,p);
    return;
}
inline int query(int nl,int nr,int l,int r,int k){
    if(l==r)return l;
    int delta=tr[tr[nr].l].sum-tr[tr[nl].l].sum;
    int mid=(l+r)>>1;
    if(delta>=k)return query(tr[nl].l,tr[nr].l,l,mid,k);
    else return query(tr[nl].r,tr[nr].r,mid+1,r,k-delta);
}
inline void LSH(){
    m=n;
    sort(b+1,b+m+1);
    m=unique(b+1,b+m+1)-b-1;
    for(int i=1;i<=n;i++){
    a[i]=lower_bound(b+1,b+m+1,a[i])-b;
    }
    return;
}
int main(){
    n=read();
    q=read();
    for(int i=1;i<=n;i++)a[i]=b[i]=read();
    LSH();
    for(int i=1;i<=n;i++)insert(rt[i-1],rt[i],1,m,a[i]);
    for(int i=1;i<=q;i++){
    int l=read(),r=read(),k=read();
    printf("%d\n",b[query(rt[l-1],rt[r],1,m,k)]);
    }
    return 0;
}