class Solution {
    ArrayList<Integer> countDistinct(int k, int arr[]) {
        // code here
        ArrayList<Integer> al=new ArrayList<>();
        for(int i=0;i<=arr.length-k;i++){
            HashSet<Integer> hs=new HashSet<>();
            for(int j=i;j<i+k;j++){
                hs.add(arr[j]);
            }
            al.add(hs.size());
        }
        return al;
    }
}
======================================================
[1, 2, 1, 3, 4, 2, 3]

strat=0
end=0

first i will count how many distinct elemnts are there each time i increment end pointer



class Solution {
    ArrayList<Integer> countDistinct(int k, int arr[]) {
        // code here
        
        int start=0;
        int end=0;
        HashMap<Integer,Integer> hm=new HashMap<>();
        ArrayList<Integer> al=new ArrayList<>();
        int dist=0;
        int x=0;
        for(int i=0;i<k;i++){
            if(hm.containsKey(arr[i])){
                 x=hm.get(arr[i]);
                x++;
                hm.put(arr[i],x);
            }else{
                hm.put(arr[i],1);
                dist++;
            }
            end++;
        }
        al.add(dist);
        for(int i=k;i<arr.length;i++){
             x=hm.get(arr[start]);
            x--;
            hm.put(arr[start],x);
            if(hm.get(arr[start])==0){
                hm.remove(arr[start]);
                dist--;
            }
            start++;
            //----------------
            if(hm.containsKey(arr[i])){
                 x=hm.get(arr[i]);
                x++;
                hm.put(arr[i],x);
            }else{
                hm.put(arr[i],1);
                dist++;
            }
            
            al.add(hm.size());
            
        }
        return al;
        //O(k)+O(n)=0(k)
    }
    //0((n-k)*k)=O(n*k-k^2)=O(n*k)~0(n^2)
}
==============================================