head of a linked list and a value
x, partition it such that all nodes less than
x come before nodes greater than or equal to
You should preserve the original relative order of the nodes in each of the two partitions.
Input: head = [1,4,3,2,5,2], x = 3 Output: [1,2,2,4,3,5]
Input: head = [2,1], x = 2 Output: [1,2]
-100 <= Node.val <= 100
-200 <= x <= 200