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}

.

先通过快慢指针找到转换节点，将转换节点后半部分逆序，然后再将转换节点依次插入前半部分即可。

代码如下：

/**
* 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 || !head->next)
return;

ListNode* p1,*p2;
p1 = p2 = head;
while(p2->next && p2->next->next)
{
p1 = p1->next;
p2 = p2->next->next;
}

ListNode* cur = p1->next;
ListNode* next;
while(cur->next)
{
next = cur->next;
cur->next=next->next;
next->next = p1->next;
p1->next = next;
}

p2 = head;
cur = p1->next;
while(p2!=p1)
{
p1->next = cur->next;
cur->next = p2->next;
p2->next = cur;
p2 = cur->next;
cur = p1->next;
}

}
};