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;

}