private void validateInput(ListNode<Integer> list) {
    if (list == null) throw new IllegalArgumentException("You can't pass a null list as argument.");
  }
Iterative algorithm to solve this problem. Using two pointer to the element before the value
and after the value we are going to create two list and merge it at the end of this algorithm.
The complexity order is equals to O(N) in time terms and O(1) in space terms because we are
not
using any auxiliary data structure to solve this problem.
src/main/java/com/github/pedrovgs/problem60/PartitionList.java