leetcode之Reorder List

Given a singly linked list L: L0→L1→…→Ln-1→Ln,
reorder it to: L0→Ln→L1→Ln-1→L2→Ln-2→…

You must do this in-place without altering the nodes' values.

For example,
Given {1,2,3,4}, reorder it to {1,4,2,3}.

这道题分三步：

1：首先将原来的链表拆分成两部分，用next和next.next分

2：将第二部分链表反转

3：将第一部分链表和第二部分反转了的链表merge

Takeaway Messages from This Problem

The three steps can be used to solve other problems of linked list. A little diagram may help better understand them.

Reverse List:

Merge List:

下面附上程序源码：

public void reorderList(ListNode head) {if(head == null || head.next==null)  {  return;  }  ListNode walker = head;  ListNode runner = head;  while(runner.next!=null && runner.next.next!=null)  {  walker = walker.next;  runner = runner.next.next;  }  ListNode head1 = head;  ListNode head2 = walker.next;  walker.next = null;  head2 = reverse(head2);  while(head1!=null && head2!=null)  {  ListNode next = head2.next;  head2.next = head1.next;  head1.next = head2;  head1 = head2.next;  head2 = next;  }  }private ListNode reverse(ListNode head)  {  ListNode pre = null;  ListNode cur = head;  while(cur!=null)  {  ListNode next = cur.next;  cur.next = pre;  pre = cur;  cur = next;  }  return pre;  }

转载于:https://www.cnblogs.com/gracyandjohn/p/4432402.html

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