leetcode——チェーンテーブルreorder

#include <iostream>
using namespace std;
  struct ListNode {
      int val;
      ListNode *next;
      ListNode(int x) : val(x), next(NULL) {}
  };
 
class Solution {
public:
    void reorderList(ListNode *head) {
        
        ListNode * p0 = head;
        ListNode * p = head;
        if(  !(p != NULL && p->next != NULL && p->next->next != NULL)){
            //        
            return;
        }
        
        //     
        while( p->next!= NULL && p->next->next != NULL){
        	p0 = p0->next;
            p = p->next->next;
        }
        //    
        p = p0->next;
        p0->next = NULL;
        
		//   
        ListNode *t = p;
		p = p->next;
		t->next = NULL;//    
        while(p != NULL){
            ListNode *tt = p->next;
            p->next = t;
            t = p;
            p = tt;
        }
        p = t;
        
        //     。
        ListNode *tt;
        p0 = head;
        while( p0 != NULL && p!= NULL){
            t = p0->next;
            tt = p->next;
            p0->next = p;
            p->next = t;
            p0 = t;
            p = tt;
        }
    }
};
int main()
{
Solution ss;
	ListNode *head  = new ListNode(1);
	ListNode *p = head;
	int n = 2;
	while( n != 6)
	{
		p->next = new ListNode(n++);
		p = p->next;
	}

	ss.reorderList(head);
	return 0;
}