首页 > 代码库 > LeetCode解题报告:Reorder List

LeetCode解题报告:Reorder List

2024-07-08 17:13:39   221人阅读

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}.

思路：

1.利用快慢两个指针将链表一分为二；

2.针对第二个子链表求倒序；

3.利用merge思想将两个子链表合并。

代码：

 1 public class ReorderSingleList { 2     /** 3      * Definition for singly-linked list. class ListNode { int val; ListNode 4      * next; ListNode(int x) { val = x; next = null; } } 5      */ 6     public void reorderList(ListNode head) { 7         if (head == null || (head.next == null)) { 8             return; 9         }10         // fast and slow point find the mid position.11         ListNode fast = head;12         ListNode slow = head;13         while ((fast != null) && (fast.next != null)) {14             fast = fast.next.next;15             slow = slow.next;16         }17 18         // reverse the last second list.19         ListNode headnode = new ListNode(-1);20         headnode.next = slow;21         ListNode temp = headnode.next;22         while (temp.next != null) {23             ListNode insert = temp.next;24             ListNode currNext = insert.next;25             insert.next = headnode.next;26             headnode.next = insert;27             temp.next = currNext;28         }29 30         // merge insert31         ListNode firstcur = head;32         ListNode secondcur = headnode.next;33         while (firstcur != slow && (secondcur != slow)) {// at first,I make a mistake in here;34             ListNode firstnex = firstcur.next;35             ListNode secondnex = secondcur.next;36             firstcur.next = secondcur;37             secondcur.next = firstnex;38             firstcur = firstnex;39             secondcur = secondnex;40         }41     }42 43     public static void main(String[] args) {44         ListNode t5 = new ListNode(5);45         ListNode t4 = new ListNode(4, t5);46         ListNode t3 = new ListNode(3, t4);47         ListNode t2 = new ListNode(2, t3);48         ListNode t1 = new ListNode(1, t2);49         new ReorderSingleList().reorderList(t1);50         System.out.println(t1);51     }52 53 }
View Code

 


联系
我们