143.Reorder List
143.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}.
https://leetcode.com/problems/reorder-list/description
https://leetcode.com/problems/reorder-list/description
/*
143.Reorder List
, 。 ,
O(n)
*/
class Solution{
pubilic:
void recorderList(ListNode* head){
if(!head || !head->next) return;
ListNode *slow = head, *fast = head, *p=head, *q=head;
while(fast->next && fast->next->next)
slow = slow->next,slow->next = NULL;
fast = slow->next,slow->next = NULL;
p = fast, q = fast->next, fast->next = NULL;
while(q)
{
auto tem = q->next;
q->next = p;
p = q, q = tem;
}
q = head;
while(q&&p)
{
auto tem1 = q->next, tem2 = p->next;
p->next = q->next;
q->next = p;
q = tem1, p = tem2;
}
}
}