Count distinct elements in every window.cpp

class Solution {
  public:
    vector<int> countDistinct(vector<int> &arr, int k) {
        // code here.
        int n=arr.size();
        unordered_map<int, int>mp;
        for(int i=0;i<k;i++) mp[arr[i]]++;
        
        vector<int>ans;
        ans.push_back(mp.size());
        
        for(int i=k;i<n;i++){
            mp[arr[i]]++;
            mp[arr[i-k]]--;
            
            if(mp[arr[i-k]]==0){
                mp.erase(arr[i-k]);
            }
            
            ans.push_back(mp.size());
        }
        return ans;
    }
};