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LeetCode: Reorder List
LeetCode: 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}.
地址：https://oj.leetcode.com/problems/reorder-list/
算法：先把链表从中间节点分成两段，然后将后半部分的链表逆置，最后在将后半部分的链表按题目的要求插入原链表中。代码：
1 /** 2 * Definition for singly-linked list. 3 * struct ListNode { 4 * int val; 5 * ListNode *next; 6 * ListNode(int x) : val(x), next(NULL) {} 7 * }; 8 */ 9 class Solution {10 public:11 void reorderList(ListNode *head) {12 int num_node = 0;13 ListNode *p = head;14 while(p){15 ++num_node;16 p = p->next;17 }18 int half_num_node = (num_node + 1) / 2;19 p = head;20 ListNode *pre = NULL;21 for (int i = 0; i < half_num_node; ++i){22 pre = p;23 p = p->next;24 }25 if(pre) pre->next = NULL;26 pre = NULL;27 ListNode *half_head = NULL;28 while (p){29 pre = p;30 p = p->next;31 pre->next = half_head;32 half_head = pre;33 }34 p = head;35 while(half_head){36 pre = half_head;37 half_head = half_head->next;38 pre->next = p->next;39 p->next = pre;40 p = p->next->next;41 }42 }43 };
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