[LeetCode]97. Reorder List链表重排序

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}

{1,4,2,3}

Subscribe to see which companies asked this question

/**
* Definition for singly-linked list.
* struct ListNode {
*     int val;
*     ListNode *next;
*     ListNode(int x) : val(x), next(NULL) {}
* };
*/
class Solution {
public:
void reorderList(ListNode* head) {
if(head == NULL || head->next == NULL) return;
ListNode *slow = head, *fast = head;
while(fast->next != NULL && fast->next->next != NULL) {
slow = slow->next;
fast = fast->next->next;
}
ListNode* head1 = head;
ListNode* head2 = slow->next;
head2 = reverseList(head2);
slow->next = NULL;
while(head2 != NULL) {
ListNode *next1 = head1->next, *next2 = head2->next;
head1->next = head2;
head2->next = next1;
head1 = next1;
head2 = next2;
}
}
private:
ListNode* reverseList(ListNode* head) {
ListNode* rHead = NULL;
ListNode* curr = head;
ListNode* pTail = NULL;
while(curr != NULL) {
ListNode* pNext = curr->next;
if(pNext == NULL)
rHead = curr;
curr->next = pTail;
pTail = curr;
curr = pNext;
}
return rHead;
}
};

转载于:https://www.cnblogs.com/aprilcheny/p/5018498.html