K_Frequent_Elements

# K frquent element

class Solution {
    public int[] topKFrequent(int[] nums, int k) {
        
        Map<Integer,Integer> map=new HashMap<>();
        int result[]=new int[k];
        for(int x:nums)
        {
            map.put(x,map.getOrDefault(x,0)+1);
        }
       List<Integer> list=new ArrayList<>(map.keySet());
       
       Collections.sort(list,(a,b)->
       map.get(b)-map.get(a));
        // Arrays.sort(obj,-1);
       for(int i=0;i<k;i++)
       {    result[i]=list.get(i);
       }

        return result;
    }
}

/*
Explaination:
(a,b) -> map.get(b) - map.get(a) is a lambda expression, Also known as a comparator.

It's defining the 'priority' of the queue to be whichever number ( a or b ) is bigger.

It works like this...

If (a,b) -> map.get(b) - map.get(a) - It will start adding elements with their freq in decreasing order (in this case, it will be 3 2 1 (freq))
if (a,b) -> map.get(a) - map.get(b) - It will start adding element with their freq in increasing order (in this case, it will be 1 2 3 (freq))

// Since you are always doing map.get, it means you're comparing it on values only, so doesn't confuse it with whatever is written in the key
*/