you need to use insert and delete instead of sort to decrease complexity

#include <bits/stdc++.h>
#define int long long

using namespace std;
float median(vector<int> &a, int d)
{
    float median ;
    if(d%2==0)
    {
       int m1=d/2-1;
       median = (a[m1]+a[m1+1]);
    }
    else
    {
        median= a[d/2]*2;
    }
    return median;
}

signed main()
{
    int n, d;
    int cnt=0;
    cin>>n>>d;
    vector<int> a(d);
    vector<int> mark(n+1);
    for(int i=0;i<d;i++){
    cin>>a[i];mark[i]=a[i];}
    sort(a.begin(),a.end());
    for(int i=d;i<n;i++)
    {
        int temp;cin>>temp;
        mark[i]=temp;
        float me = median(a,d);
        if(temp>=me)cnt++;
        auto it = lower_bound(a.begin(), a.end(), mark[i-d]);
        a.erase(it);
        auto m = lower_bound(a.begin(), a.end(), temp);
        a.insert(m,temp);

    }
    cout<<cnt;
}