[LeetCode] Odd Even Linked List

[LeetCode] Odd Even Linked List

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.

You shocould try to do it in place. The program shocould run in O (1) space complexity and O (nodes) time complexity.

Example:
Given1->2->3->4->5->NULL,
Return1->3->5->2->4->NULL.

Note:
The relative order inside both the even and odd groups shocould remain as it was in the input.
The first node is considered odd, the second node even and so on...

Solutions

Connect the nodes at the odd and even locations, and connect the odd and even linked lists.

Implementation Code

//Runtime: 1 ms/** * Definition for singly-linked list. * public class ListNode { *     int val; *     ListNode next; *     ListNode(int x) { val = x; } * } */public class Solution {    public ListNode oddEvenList(ListNode head) {        if (head == null || head.next == null) {            return head;        }        ListNode oddTail = head;        ListNode even = head.next;        ListNode evenTail = even;        int i = 1;        ListNode cur = head.next.next;        while (cur != null) {            if (i++ % 2 == 1) {                oddTail.next = cur;                oddTail = oddTail.next;            } else {                evenTail.next = cur;                evenTail = evenTail.next;            }            cur = cur.next;        }        evenTail.next = null;        oddTail.next = even;        return head;    }}