Given the head of a linked list containing k distinct elements, return the head to a linked list of length k containing the frequency of each distinct element in the given linked list in any order.
Example 1:
Input: head = [1,1,2,1,2,3]
Output: [3,2,1]
Explanation: There are 3 distinct elements in the list. The frequency of 1 is 3, the frequency of 2 is 2 and the frequency of 3 is 1. Hence, we return 3 -> 2 -> 1.
Note that 1 -> 2 -> 3, 1 -> 3 -> 2, 2 -> 1 -> 3, 2 -> 3 -> 1, and 3 -> 1 -> 2 are also valid answers.
Example 2:
Input: head = [1,1,2,2,2]
Output: [2,3]
Explanation: There are 2 distinct elements in the list. The frequency of 1 is 2 and the frequency of 2 is 3. Hence, we return 2 -> 3.
Example 3:
Input: head = [6,5,4,3,2,1]
Output: [1,1,1,1,1,1]
Explanation: There are 6 distinct elements in the list. The frequency of each of them is 1. Hence, we return 1 -> 1 -> 1 -> 1 -> 1 -> 1.
Constraints:
[1, 105].1 <= Node.val <= 105[1,1,2,1,2,3]