hdu 2665 划分树

開始用线段树+归并排序，4700+ms飘过~，后来去学划分树。尽管还不是非常懂，只是就这样吧

#include<iostream>
#include<algorithm>
#define maxn 100010
using namespace std;
int n,m;
int nsort[maxn];
int nleft[30][maxn],tree[30][maxn];
void build(int l,int r,int c)
{
	if(l==r) return;
	int mid=(l+r)/2;
	int sum=mid-l+1;
	for(int i=l;i<=r;i++)
	{
		if(tree[c][i]<nsort[mid]) sum--;
	}
	int ll=l,rr=mid+1;
	for(int i=l;i<=r;i++)
	{
		if(tree[c][i]<nsort[mid]) tree[c+1][ll++]=tree[c][i];
		else if(tree[c][i]==nsort[mid]&&sum>0) tree[c+1][ll++]=tree[c][i],sum--;
		else tree[c+1][rr++]=tree[c][i];
		nleft[c][i]=nleft[c][l-1]+ll-l;
	}
	build(l,mid,c+1);
	build(mid+1,r,c+1);
}
int que(int l,int r,int a,int b,int k,int c)
{
	if(a==b) return tree[c][a];
	int mid=(l+r)/2;
	int cnt=nleft[c][b]-nleft[c][a-1];
	if(cnt>=k)
	{
		int nl=l+nleft[c][a-1]-nleft[c][l-1];
		int nr=nl+cnt-1;
		return que(l,mid,nl,nr,k,c+1);
	}
	else 
	{
		int nr=b+nleft[c][r]-nleft[c][b];
        int nl=nr-(b-a-cnt);
        return que(mid+1,r,nl,nr,k-cnt,c+1);
	}
}
int main()
{
	cin.sync_with_stdio(false);
	int t;
	cin>>t;
	while(t--)
	{
		cin>>n>>m;
		for(int i=1;i<=n;i++)
		{
			cin>>tree[0][i];
			nsort[i]=tree[0][i];
		}
		sort(nsort+1,nsort+n+1);
		build(1,n,0);//l,r,层。 
		while(m--)
		{
			int a,b,k;
			cin>>a>>b>>k;
			cout<<que(1,n,a,b,k,0)<<endl;
		}
	}
	return 0;
}