[Leetcode] #143 Reorder List

Discription:

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}.

Solution:

void reorderList(ListNode* head) {if (head == NULL || head->next == NULL) return ;ListNode *pslow = head;ListNode *pfast = head;while (pfast->next && pfast->next->next){pslow = pslow->next;pfast = pfast->next->next;}ListNode *last= pslow->next;pslow->next = NULL;ListNode *pre = NULL;while (last){ListNode *post = last->next;last->next = pre;pre = last;last = post;}ListNode *node1 = head, *node2 = pre;while (node2 != NULL){ListNode *tmp1 = node1->next;ListNode *tmp2 = node2->next;node1->next = node2;node2->next = tmp1;node1 = tmp1;node2 = tmp2;}}

附：Leetcode源代码见我的GitHub