poj 2104 划分树

思路：裸的划分树

#include<iostream>
#include<algorithm>
#include<cstring>
#include<cstdio>
#include<vector>
#define Maxn 100010
#define lson(x) x<<1
#define rson(x) x<<1|1
using namespace std;
int n,m,val[20][Maxn],toLeft[20][Maxn],sorted[Maxn];
struct Tree{
    int l,r;
    int mid(){
        return (l+r)>>1;
    }
}tree[Maxn*4];
void BuildTree(int l,int r,int dep,int po)
{
    tree[po].l=l,tree[po].r=r;
    if(l==r)
        return ;
    int mid=tree[po].mid();
    int lpos=l,rpos=mid+1;
    int same=mid-l+1,i;
    for(i=l;i<=r;i++){
        if(val[dep][i]<sorted[mid])
            same--;
    }
    for(i=l;i<=r;i++){
        if(i==l) toLeft[dep][i]=0;
        else toLeft[dep][i]=toLeft[dep][i-1];
        if(val[dep][i]<sorted[mid]){
            val[dep+1][lpos++]=val[dep][i],toLeft[dep][i]++;
        }
        else
        if(val[dep][i]>sorted[mid]){
            val[dep+1][rpos++]=val[dep][i];
        }
        else
        if(same){
            val[dep+1][lpos++]=val[dep][i],toLeft[dep][i]++,same--;
        }
        else
            val[dep+1][rpos++]=val[dep][i];
    }
    BuildTree(l,mid,dep+1,lson(po));
    BuildTree(mid+1,r,dep+1,rson(po));
}
int query(int l,int r,int k,int dep,int po)
{
    //cout<<tree[po].l<<" "<<tree[po].r<<endl;
    if(l==r)
        return val[dep][l];
    int ls,lns;
    if(l==tree[po].l){
        ls=toLeft[dep][r];
        lns=0;
    }else{
        ls=toLeft[dep][r]-toLeft[dep][l-1];
        lns=toLeft[dep][l-1];
    }
    int mid=tree[po].mid();
    if(ls>=k){
        int newl=tree[po].l+lns;
        int newr=tree[po].l+lns+ls-1;
        return query(newl,newr,k,dep+1,lson(po));
    }
    else{
        int rns=l-tree[po].l-lns;
        int rs=r-l+1-ls;
        int newl=mid+1+rns;
        int newr=mid+rns+rs;
        return query(newl,newr,k-ls,dep+1,rson(po));
    }
}
int main()
{
    int i,j,a,b,k;
    while(scanf("%d%d",&n,&m)!=EOF)
    {
        for(i=1;i<=n;i++){
            scanf("%d",&val[0][i]);
            sorted[i]=val[0][i];
        }
        sort(sorted+1,sorted+1+n);
        BuildTree(1,n,0,1);
        for(i=0;i<m;i++){
            scanf("%d%d%d",&a,&b,&k);
            printf("%d
",query(a,b,k,0,1));
        }
    }
    return 0;
}