86. Partition List

https://leetcode.com/problems/partition-list/

Python

class Solution:
    def partition(self, head: Optional[ListNode], x: int) -> Optional[ListNode]:
        front_head = ListNode()
        after_head = ListNode()

        front_cur, after_cur = front_head, after_head
        cur = head

        while cur:
            if cur.val < x:
                front_cur.next = cur
                front_cur = front_cur.next
            else:
                after_cur.next = cur
                after_cur = after_cur.next
            cur = cur.next

        after_cur.next = None
        front_cur.next = after_head.next

        return front_head.next

Javascript

var partition = function(head, x) {
  let lessHeader = new ListNode();
  let less = lessHeader;

  let greaterHeader = new ListNode();
  let greater = greaterHeader;

  while (head !== null) {
    if (head.val < x) {
      less.next = head;
      less = less.next;
    } else {
      greater.next = head;
      greater = greater.next;
    }

    head = head.next;
  }

  greater.next = null;

  less.next = greaterHeader.next;

  return lessHeader.next;
};