hdu2665

链接：点击打开链接

题意：求给定区间中第k小的数

代码：

#include<stdio.h>
#include<iostream>
#include<string.h>
#include<algorithm>
using namespace std;
const int SIZE=100005;
int tmp[SIZE],toleft[50][SIZE];
int tree[50][SIZE];
void build(int l,int r,int rt){
    int i,mid,sum,lpos,rpos;
    if(l==r)
    return;
    mid=(l+r)>>1;
    sum=mid-l+1;
    for(i=l;i<=r;i++)
    if(tree[rt][i]<tmp[mid])
    sum--;
    lpos=l,rpos=mid+1;
    for(i=l;i<=r;i++){
        if(tree[rt][i]<tmp[mid])
        tree[rt+1][lpos++]=tree[rt][i];
        else if(tree[rt][i]==tmp[mid]&&sum>0){
            tree[rt+1][lpos++]=tree[rt][i];
            sum--;
        }
        else
        tree[rt+1][rpos++]=tree[rt][i];
        toleft[rt][i]=toleft[rt][l-1]+lpos-l;
    }
    build(l,mid,rt+1);
    build(mid+1,r,rt+1);
}
int query(int L,int R,int k,int l,int r,int rt){
    int mid,newl,newr,cnt;
    if(L==R)
    return tree[rt][L];
    mid=(l+r)>>1;
    cnt=toleft[rt][R]-toleft[rt][L-1];
    if(cnt>=k){
        newl=l+toleft[rt][L-1]-toleft[rt][l-1];
        newr=newl+cnt-1;
        return query(newl,newr,k,l,mid,rt+1);
    }
    else{
        newr=R+toleft[rt][r]-toleft[rt][R];
        newl=newr-(R-L-cnt);
        return query(newl,newr,k-cnt,mid+1,r,rt+1);
    }
}                                                   //划分树模板
int main(){                                         //详见poj2104
    int t,n,m,i,a,b,c;                              //http://blog.csdn.net/stay_accept/article/details/50492052
    scanf("%d",&t);
    while(t--){
        scanf("%d%d",&n,&m);
        memset(tree,0,sizeof(tree));
        for(i=1;i<=n;i++){
            scanf("%d",&tree[0][i]);
            tmp[i]=tree[0][i];
        }
        sort(tmp+1,tmp+n+1);
        build(1,n,0);
        while(m--){
            scanf("%d%d%d",&a,&b,&c);
            printf("%d\n",query(a,b,c,1,n,0));
        }
    }
    return 0;
}