Leetcode: 328. Odd Even Linked List(JAVA)

【问题描述】

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

Example:

Given 

1->2->3->4->5->NULL

,

return 

1->3->5->2->4->NULL

.

Note:

The relative order inside both the even and odd groups should remain as it was in the input. 

The first node is considered odd, the second node even and so on ...

【思路】

维护两个指针，odd与even，odd指针奇数相连，even偶数相连，evenHead指向head.next即even的头。

public class Solution {
public ListNode oddEvenList(ListNode head) {
if(head == null || head.next == null)
return head;

ListNode odd = head, even = head.next, evenHead = head.next;
while(even != null && even.next != null){
odd.next = even.next;
odd = odd.next;
even.next = odd.next;
even = even.next;
}
odd.next = evenHead;
return head;

}
}