In last Div. 4 contest, my solution for problem Problem F received TLE verdict in testcase 18 during the system test. Later on I found that, changing unordered_map to map works fine to achieve Accepted verdict.

Code:

void solve()
{   

int n, k; cin >> n >> k ; 
vi g; 
unordered_map<int, int> m; 
for(int i = 0; i<n; i++)
{
  int a; cin >> a; 
  m[a]++; 
}

for(auto &x: m)
{
  if(x.second>=k) 
  {
      g.pb(x.first); 
  }
}

if(g.size()==0) { cout << -1 << "\n"; return; }


sort(g.begin(), g.end()); 

int l = 0, r = -1, cl = g[0]; 
  n = g.size(); 
  for(int i = 1; i<n; i++)
  {
      if(g[i] &mdash; g[i-1]>1)
      {
        if(r &mdash; l <= g[i-1] &mdash; cl)
        {
          r = g[i-1]; 
          l = cl; 
        }

        cl = g[i]; 
      }
  }

 if(g[n-1] &mdash; cl >= r &mdash; l )
    {
      r = g[n-1]; l = cl; 
    }

    cout << l << " " << r << '\n'; 

}

So far I know, when we do not need the elements to be ordered, we should use unordered_map which is the case in this problem. So why std::map works better than std::unordered_map in terms of time complexity?

Thanks for your patience!