99. 重排链表
难度系数 中等 通过率 24%
给定一个单链表L: L0→L1→…→Ln-1→Ln,
重新排列后为：L0→Ln→L1→Ln-1→L2→Ln-2→…
必须在不改变节点值的情况下进行原地操作。
样例
给出链表 1->2->3->4->null，重新排列后为1->4->2->3->null
/**
* Definition of ListNode
* class ListNode {
* public:
* int val;
* ListNode *next;
* ListNode(int val) {
* this->val = val;
* this->next = NULL;
* }
* }
*/
class Solution {
public:
/*
* @param head: The head of linked list.
* @return: nothing
*/
void reorderList(ListNode * head) {
// write your code here
if (head == nullptr || head->next == nullptr)
{
return;
}
ListNode *slow = head, *fast = head->next;
while(fast&&fast->next)
{
slow = slow->next;
fast = fast->next->next;
}
fast = slow->next;
slow->next = nullptr;
ListNode *rHead = nullptr;
while (fast)
{
ListNode *r = fast->next;
fast->next = rHead;
rHead = fast;
fast = r;
}
fast = rHead;
slow = head;
while(slow&&fast)
{
ListNode *rr = fast->next;
ListNode *lr = slow->next;
fast->next = lr;
slow->next = fast;
fast = rr;
slow = lr;
}
}
};
