CAMC - solution

#include <bits/stdc++.h>
using namespace std;

vector<pair<long long int,long long int > >vec;
vector<long long int> mark(100009);
vector<long long int >sample(100009);
unordered_map<long long int ,long long int >org;




 /* We would first mark all the vector elements with their respective colors and as for every M elements they are unique
    so it will just repeat as 1,2,3....m,1,2,3... */

  void init(long long int  N, long long int  M)
  {
        long long int  it=1;
        for(long long int  i=0;i<N;i++)
        {
            mark[i]=it;
            it++;
            if(it>M)
            {
               it=1;
            }}}

 /* Now I will pair their color with the actual numbers, mark vector can be excluded and this process can be dN in a
    single loop for memory efficiency but I have dN this for simplicity */

  void filling(long long int N)
  {
      for(long long int  i=0;i<N;i++)
        {
            vec.push_back(make_pair(sample[i],mark[i]));
        }
  }

  /*Initialsing first k elements in the map to cover cases with k or more than k elements with same value (answer will be 0 in that case)*/

  void gut(long long int  M)
  {

       for(long long int  i=0;i<M;i++)
            org[vec[i].second]++;
  }


  void solve(long long int  N, long long int  M)
  {
       long long int  final_answer=INT_MAX;
       long long int  forv=0; /* first iterator*/
       long long int  backw=M-1; /* second iterator*/
       long long int  height=0; /* calculating variable*/
       gut(M);
       if(org.size()==M)
       {
           height=vec[backw].first-vec[forv].first;
           final_answer = min(height,final_answer);
       }
       while(1)
       {
           if(org.size()==M)
           {
               long long int  height = vec[backw].first-vec[forv].first; /* check for minimum value */
               final_answer=min(final_answer,height);
               org[vec[forv].second]--; /* Now we will increase the first iterator until we get to the point where the map size again becomes<M and that point will be the minimum value */
               if(org[vec[forv].second]==0) org.erase(vec[forv].second); /* once we have one colour completed, we would delete this from the map*/
               forv++;
           }
           else
           {
               backw++; /* we increase the second iterator till we get the map size == M */
               if(backw>vec.size()-1)
                  break;
               org[vec[backw].second]++;}} /* also we will keep adding the colour */
        cout << final_answer << endl;
        final_answer=INT_MAX;
        org.clear();
        sample.clear();
        mark.clear();
        vec.clear();
  }
  int main()
  {
    ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
    long long int  test;
    cin >> test;
    while(test--)
    {
        long long int  N,M;
        cin >> N >> M;
        for(long long int  i=0;i<N;i++)
        {
            cin >> sample[i];
        }
        init(N,M);
        filling(N);
        sort(vec.begin(),vec.end()); /* sorting to get the the difference easily as  Arr[k]-Arr[0] is always less than Arr[k+1]-Arr[0] */
        vector<long long int >point;
        for(long long int  i=0;i<N;i++)
            point.push_back(vec[i].second);

        solve(N,M);
    }
    return 0;
}