hdu 2665 Kth number_划分树

题意：求区间【a，b】的第k大

因为多次询问要用到划分树

#include <iostream>
#include<cstdio>
#include<algorithm>
#include<cstring>
using namespace std;
#define MAXN 100010
int tree[30][MAXN],sorted[MAXN];
int toleft[30][MAXN];
void build(int l,int r,int dep){
	if(l==r)return;
	int i;
	int mid=(l+r)>>1;
	int same=mid-l+1;
	for(i=l;i<=r;i++)
		if(tree[dep][i]<sorted[mid])
			same--;
	int lpos=l;
	int rpos=mid+1;
	for(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;//左边的个数
	}
	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 argc, char** argv) {
	int v,n,m,i;
	int s,t,k;
	scanf("%d",&v);
	while(v--){
		scanf("%d%d",&n,&m);
		memset(tree,0,sizeof(tree));
		memset(toleft,0,sizeof(toleft));
		for(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--){
			scanf("%d%d%d",&s,&t,&k);
			printf("%d\n",query(1,n,s,t,0,k));
		}
	}
	return 0;
}