Reorder List

题目链接：

https://leetcode.com/problems/reorder-list/description/

描述

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.

输入

For example,
Given {1,2,3,4},

输出

reorder it to {1,4,2,3}.

样例输入

样例输出

算法思想：

先把表等分成a与b两个链表，然后把b逆序，最后把a和b链表交叉合并起来即可

源代码

class Solution {public:    void reorderList(ListNode* head) {        if (!head)            return ;        ListNode *a, *b;        //分离链表分成一半一半        a = head;        b = head->next;        while (b)        {            b = b->next;            if (b)            {                a = a->next;                b = b->next;            }        }        b = a->next;        a->next = NULL;        a = head;        //让b链表逆序        if (b)        {            ListNode *current = b->next;            ListNode *tem = current;            b->next = NULL;            while (current)            {                current = current->next;                tem->next = b;                b = tem;                tem = current;            }        }        //合并2个链表        ListNode *a1, *a2, *b1;        a1 = a; a2 = a1->next;        b1 = b;        while (b)        {            b = b->next;            a1->next = b1;            b1->next = a2;            b1 = b;            a1 = a2;            if (a1)                a2 = a1->next;        }    }};

最优源代码

算法复杂度：