86. Partition List

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

JavaScript

/**
 * Definition for singly-linked list.
 * function ListNode(val) {
 *     this.val = val;
 *     this.next = null;
 * }
 */
/**
 * @param {ListNode} head
 * @param {number} x
 * @return {ListNode}
 */
var partition = function(head, x) {
  var ltHead = new ListNode()
  var geHead = new ListNode()
  var lt = ltHead
  var ge = geHead

  while (head) {
    if (head.val < x) {
      lt.next = head
      lt = lt.next
    } else {
      ge.next = head
      ge = ge.next
    }
    head = head.next
  }

  ge.next = null
  lt.next = geHead.next
  return ltHead.next
}

Python

# Definition for singly-linked list.
# class ListNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.next = None


class Solution(object):

    def partition(self, head, x):
        """
        :type head: ListNode
        :type x: int
        :rtype: ListNode
        """
        lt = ltHead = ListNode(None)
        ge = geHead = ListNode(None)

        while head:
            if head.val < x:
                lt.next = head
                lt = lt.next
            else:
                ge.next = head
                ge = ge.next
            head = head.next

        ge.next = None
        lt.next = geHead.next
        return ltHead.next