2016秋季练习

来源：POJ2104

划分树：

#include<iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;
int n,Qm;
const int MAXN = 100010;
int a[MAXN];
int tree[20][MAXN];
int tol[20][MAXN];
void build(int dep,int l,int r){
    if(l == r) return ;
    int mid = (l+r)>>1;
    int same = mid-l+1;
    for(int i=l;i<=r;i++) {
        if(tree[dep][i] < a[mid]) same -- ;
    }
    int lpos = l;
    int rpos = mid+1;
    for(int i=l;i<=r;i++) {
        if(tree[dep][i] < a[mid])
            tree[dep+1][lpos++] = tree[dep][i];
        else if(tree[dep][i] == a[mid] && same > 0){
            tree[dep+1][lpos++] = tree[dep][i];
            same -- ;
        }
        else
            tree[dep+1][rpos++] = tree[dep][i];
        tol[dep][i] = tol[dep][l-1]+lpos-l;
    }
    build(dep+1,l,mid);
    build(dep+1,mid+1,r);
}
int query(int left,int right,int l,int r,int dep,int k){
//    cout<<left<<" "<<right<<" "<<l<<" "<<r<<" "<<dep<<endl;
    if(l == r) return tree[dep][l];
    int mid = (left+right)>>1;
    int cnt = tol[dep][r]-tol[dep][l-1];
    if(cnt>=k){
        int newl = left+tol[dep][l-1]-tol[dep][left-1];
        int newr = newl+cnt-1;
        return query(left,mid,newl,newr,dep+1,k);
    }
    else{
        int newr = r+tol[dep][right]-tol[dep][r];
        int newl = newr-(r-l-cnt);
        return query(mid+1,right,newl,newr,dep+1,k-cnt);
    }

}
int main(){
    int l,r,k;
    while(scanf("%d%d",&n,&Qm)==2){
        memset(tree,0,sizeof tree);
        for(int i=1;i<=n;i++) {
            scanf("%d",a+i);
            tree[0][i] = a[i];
        }
        sort(a+1,a+1+n);
        build(0,1,n);
        while(Qm--){
            scanf("%d%d%d",&l,&r,&k);
            printf("%d\n",query(1,n,l,r,0,k));
        }
    }
    return 0;
}