1636. Sort Array by Increasing Frequency

class Solution {
    public int[] frequencySort(int[] nums) {
        HashMap<Integer,Integer> map = new HashMap<Integer, Integer>();
        for(int i=0; i<nums.length; i++){
        if(map.containsKey(nums[i])){
            map.put(nums[i], map.get(nums[i])+1);
        }
        else{
            map.put(nums[i],1);
        }
        }
        List<Integer> list = new LinkedList<Integer>(map.keySet());
        Collections.sort(list , (a,b) ->{
            if(map.get(a) == map.get(b)){
                return b-a;
            }
            else{
                return map.get(a) - map.get(b);
            }
        });
        int[] arr = new int[nums.length];
        int index = 0;
        for(int a : list){
            for(int i=0; i<map.get(a); i++){
                arr[index++] = a;
            }
        }
        return arr;

        
    }
}