K-th Number Description You are working for Macrohard company in data structures department. After failing your previous task about key insertion you were asked to write a new data structure that would be able to return quickly k-th order statistics in the array segment. Input The first line of the input file contains n --- the size of the array, and m --- the number of questions to answer (1 <= n <= 100 000, 1 <= m <= 5 000). Output For each question output the answer to it --- the k-th number in sorted a[i...j] segment. Sample Input 7 31 5 2 6 3 7 42 5 34 4 11 7 3 Sample Output 563 Hint This problem has huge input,so please use c-style input(scanf,printf),or you may got time limit exceed. Source Northeastern Europe 2004, Northern Subregion |
Time Limit: 20000MS | | Memory Limit: 65536K |
Total Submissions: 46886 | | Accepted: 15682 |
Case Time Limit: 2000MS |
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百度搜索可持久化线段树 就出现了这道题
因为很早就知道了主席树 可惜一直没有看懂文字 无意中在bilibili弹幕网站中看到了讲算法的视频 不可思议 哈哈
我竟然在B站学算法。。。 视频地址
http://www.bilibili.com/video/av4619406
这是文字的讲解
http://seter.is-programmer.com/posts/31907.html
看完视频 按照印象。。。AC了
慢慢消化 ~
#include <stdio.h>
#include <vector>
#include <algorithm>
using namespace std;
const int maxn=1e5+5;
struct node
{
int l,r;
int sum;
}T[maxn*40];
int root[maxn],a[maxn],cnt,sum;
vector<int>v;
int getid(int x)
{
return lower_bound(v.begin(),v.end(),x)-v.begin()+1;
}
void update(int l,int r,int &x,int y,int pos)
{
T[++cnt]=T[y],T[cnt].sum++,x=cnt;
if(l==r) return ;
int mid=(l+r)/2;
if(mid>=pos) update(l,mid,T[x].l,T[y].l,pos);
else update(mid+1,r,T[x].r,T[y].r,pos);
}
int query(int l,int r,int x,int y,int k)
{
if(l==r) return l;
int mid=(l+r)/2;
int sum=T[T[y].l].sum-T[T[x].l].sum;
if(sum>=k) return query(l,mid,T[x].l,T[y].l,k);
else return query(mid+1,r,T[x].r,T[y].r,k-sum);
}
int main()
{
int n,m;
scanf("%d %d",&n,&m);
for(int i=1;i<=n;i++)
scanf("%d",&a[i]),v.push_back(a[i]);
sort(v.begin(),v.end());
v.erase(unique(v.begin(),v.end()),v.end());
for(int i=1;i<=n;i++)
update(1,n,root[i],root[i-1],getid(a[i]));
for(int i=0;i<m;i++)
{
int a,b,k;
scanf("%d %d %d",&a,&b,&k);
printf("%d\n",v[query(1,n,root[a-1],root[b],k)-1]);
}
return 0;
}