328. Odd Even Linked List

https://leetcode.com/problems/odd-even-linked-list/

JavaScript

/**
 * Definition for singly-linked list.
 * function ListNode(val) {
 *     this.val = val;
 *     this.next = null;
 * }
 */
/**
 * @param {ListNode} head
 * @return {ListNode}
 */
var oddEvenList = function(head) {
	if (!head) {
		return head;
	}

	var lastOdd = head;
	var current = head.next;
	var firstEven;

	while (current && current.next) {
		firstEven = lastOdd.next;
		lastOdd.next = current.next;
		lastOdd = lastOdd.next;
		current.next = lastOdd.next;
		lastOdd.next = firstEven;
		current = current.next;
	}

	return head;
};

Python

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


class Solution(object):

    def oddEvenList(self, head):
        """
        :type head: ListNode
        :rtype: ListNode
        """
        if not head:
            return head

        last_odd, current = head, head.next
        while current and current.next:
            first_even = last_odd.next
            last_odd.next = current.next
            last_odd = last_odd.next
            current.next = last_odd.next
            last_odd.next = first_even
            current = current.next
        return head