[LeetCode/LintCode] Odd Even Linked List

Problem

Given a singly linked list, group all odd nodes together followed by the even nodes. Please note here we are talking about the node number and not the value in the nodes.

Example

Example:
Given 1->2->3->4->5->NULL,
return 1->3->5->2->4->NULL.

Solution

public class Solution {
    /**
     * @param head: a singly linked list
     * @return: Modified linked list
     */
    public ListNode oddEvenList(ListNode head) {
        if (head != null) {
        //odd and even as two pointers, head and evenHead as two heads
            ListNode odd = head;
            ListNode even = head.next;
            ListNode evenHead = head.next;
            while (even != null && even.next != null) {
                odd.next = even.next;
                even.next = even.next.next;
                odd = odd.next;
                even = even.next;
            }
            odd.next = evenHead;
        }

        return head;
    }
}