poj2104 K-th Number

题目链接:http://poj.org/problem?id=2104

划分树模板题，模板来自于《程序设计解题策略》

#include<cstdio>
#include<iostream>
#include<cstring>
#include<algorithm>
using namespace std;
const int maxn=100010;
int tree[30][maxn];
int sorted[maxn];
int toleft[30][maxn];

void build(int l,int r,int dep)
{
	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]<sorted[mid]) same--;
	int lpos=l;
	int rpos=mid+1;
	for (int i=l;i<=r;i++)
	{
		if (tree[dep][i]<sorted[mid])  tree[dep+1][lpos++]=tree[dep][i];
		else if (tree[dep][i]==sorted[mid]&&same>0)
		{
			tree[dep+1][lpos++]=tree[dep][i];
			same--;
		}
		else tree[dep+1][rpos++]=tree[dep][i];
		toleft[dep][i]=toleft[dep][l-1]+lpos-l;
	}
	build(l,mid,dep+1);
	build(mid+1,r,dep+1);
}

int query(int L,int R,int l,int r,int dep,int k)
{
	if (l==r) return tree[dep][l];
	int mid=(L+R)>>1;
	int cnt=toleft[dep][r]-toleft[dep][l-1];
	if (cnt>=k)
	{
		int newl=L+toleft[dep][l-1]-toleft[dep][L-1];
		int newr=newl+cnt-1;
		return query(L,mid,newl,newr,dep+1,k);
	}
	else
	{
		int newr=r+toleft[dep][R]-toleft[dep][r];
		int newl=newr-(r-l-cnt);
		return query(mid+1,R,newl,newr,dep+1,k-cnt);
	}
}

int main()
{
	int n,m;
	while (~scanf("%d %d",&n,&m))
    {
		for (int i=1;i<=n;i++)
		{
			scanf("%d",&tree[0][i]);
			sorted[i]=tree[0][i];
		}
		sort(sorted+1,sorted+n+1);
		build(1,n,0);
		while (m--)
		{
			int a,b,c;
			scanf("%d %d %d",&a,&b,&c);
			printf("%d\n",query(1,n,a,b,0,c));
		}
	}
	return 0;
}