99

2017.10.23

首先遍历链表，建立两个队列，一个存放前一半一个存放后一半。

然后再遍历这两个队列，建立新的连接关系，重排链表。

/** * Definition for ListNode. * public class ListNode { *     int val; *     ListNode next; *     ListNode(int val) { *         this.val = val; *         this.next = null; *     } * } */ public class Solution {    /**     * @param head: The head of linked list.     * @return: void     */public void reorderList(ListNode head){if(head == null || head.next == null){return ;}LinkedList<ListNode> queue1 = new LinkedList<ListNode>();LinkedList<ListNode> queue2 = new LinkedList<ListNode>();//所有的节点均先入栈while(head != null){queue1.addFirst(head);head = head.next;}int i = queue1.size()/2;while(i > 0){queue2.addLast(queue1.pollFirst());i--;}head = queue1.pollLast();head.next = null;ListNode bt = head;while(!queue1.isEmpty()){queue2.peekFirst().next = queue1.peekLast();queue1.peekLast().next = bt.next;bt.next = queue2.pollFirst();bt = queue1.pollLast();}while(!queue2.isEmpty()){queue2.peekFirst().next = bt.next;bt.next = queue2.pollFirst();}}}