我在优化我的代码时遇到了一些麻烦。 某些测试用例由于“超过时间限制”而失败。 如何优化我的代码？

Question

I tried to solve a question in Hackerrank. I passed all the sample test cases but couldn't pass all the hidden test cases due to the "exceeded time limit" error. The link to the problem question is: Fraudulent-activity notification

My code is as follows.

#include <bits/stdc++.h>

using namespace std;

vector<string> split_string(string);

// Complete the activityNotifications function below.
int activityNotifications(vector<int> v, long int d) {
  long int n,ex;
  long double m;
  long int cap=v.size();
  long int notif=0;
  n=d;
  for(long int i=0;i<n&&n<cap;i++,n++)
  {
    ex=v[n];
    sort(v.begin()+i, v.begin()+i+d);
    if(d%2==0)
    {
        m=(v[(n+i-1)/2]+v[(n+i)/2])/2.0;
    }
    else
    {
        m=v[(n+i)/2];
    }
    if((m*2)>=ex)
    {
        notif++;
    }
  }
  return (notif-1);
 }
  int main()
  {
    vector<int>v;
    long int n,d;
    long int item;
    cin>>n>>d;
    for(long int i=0;i<n;i++)
    {
        cin>>item;
        v.push_back(item);
    }
    int res=activityNotifications(v,d);
    cout<<res;
    return 0;   
   }

How can I optimize this code? Please help.

Answer 1

For now, every step requires sorting with O(dlogd) time, so overall time is about O(ndlogd)

You have to minimize time for median. There is an approach with min and max heaps ( example ) to treat all data untul current moment. Median is element at the larger size heap for odd d , and average of two heaps tops for even d .

But you need median in rolling window. So possible addition: make parallel data structure ref[] (list/array working in cyclic manner) with references/pointers to heap nodes. When index leaves window (of size d ), remove corresponding node from a heap, then add new node with new value and update heaps and ref .

Every step will require only O(logd) time

Update: seems this topic contains links and descriptions of a lot of rolling window median methods