GFG PTOD | 10 Jan 2025 | Count distinct elements in every window

vector<int> countDistinct(vector<int> &arr, int k) {
        // code here.
        vector<int> res;
        unordered_map<int, int> map;
        for(int i = 0; i<k; i++)
            map[arr[i]]++;
        res.push_back(map.size());
        
        for(int i = k; i<arr.size(); i++) {
            map[arr[i]]++;
            map[arr[i-k]]--;
            
            if(map[arr[i-k]] == 0)
                map.erase(arr[i-k]);
            res.push_back(map.size());
        }
        return res;
    }