HDU:4251 The Famous ICPC Team Again(划分树)

#include <iostream>
#include <string>
#include <cstring>
#include <cctype>
#include <cstdio>
#include <map>
#include <algorithm>
using namespace std;
const int maxn=100005;
struct DivideTree
{
    int sorted[maxn],dat[20][maxn];
    int toleft[20][maxn];
    void build(int c,int L,int R)
    {
        int mid=(L+R)/2,lsame=mid+1-L,lp=L,rp=mid+1;
        for(int i=L; i<mid; ++i)
            if(sorted[i]<sorted[mid]) lsame--;
        for(int i=L; i<=R; ++i)
        {
            if(i==L)toleft[c][i]=0;
            else toleft[c][i]=toleft[c][i-1];
            if(dat[c][i]<sorted[mid])
            {
                dat[c+1][lp++]=dat[c][i];
                toleft[c][i]++;
            }
            else if(dat[c][i]>sorted[mid])
                dat[c+1][rp++]=dat[c][i];
            else
            {
                if(lsame)
                {
                    lsame--;
                    toleft[c][i]++;
                    dat[c+1][lp++]=sorted[mid];
                }
                else
                    dat[c+1][rp++]=sorted[mid];
            }

        }
        if(L==R) return ;
        build(c+1,L,mid);
        build(c+1,mid+1,R);
    }
    int query(int c,int L,int R,int ql,int qr,int k)
    {
        if(L==R) return dat[c][L];
        int mid=(L+R)/2;
        int la,lb,ra,rb;
        if(L==ql) la=0;
        else la=toleft[c][ql-1];
        lb=toleft[c][qr];
        ra=ql-L-la;
        rb=qr+1-L-lb;
        int s=lb-la;
        if(k<=s) return query(c+1,L,mid,L+la,L+lb-1,k);
        else return query(c+1,mid+1,R,mid+1+ra,mid+rb,k-s);
    }
};
DivideTree tree;
int main()
{
    int n,kase=0;
    while(scanf("%d",&n)!=EOF)
    {
        for(int i=1; i<=n; ++i)
        {
            scanf("%d",&tree.dat[0][i]);
            tree.sorted[i]=tree.dat[0][i];
        }
        sort(tree.sorted+1,tree.sorted+n+1);
        tree.build(0,1,n);
        int m;
        scanf("%d",&m);
        printf("Case %d:\n",++kase);
        while(m--)
        {
            int a,b;
            scanf("%d%d",&a,&b);
            printf("%d\n",tree.query(0,1,n,a,b,(b-a)/2+1));
        }
    }
    return 0;
}