86. Partition List

/**主要思想就是將原來的鏈表拆成2個，一個全部小於閾值，一個大於或者等於閾值，然後將後者鏈接到前者後面；
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode* partition(ListNode* head, int x) {
        if(head == NULL)
		return NULL;
	ListNode*s = new ListNode(0),*q=new ListNode(0);
	ListNode *p=s,*r=q;
	while (head!= NULL)
	{
		if (head->val < x)
		{
			s->next = head;
			s = s->next;
		}
		else
		{
			q->next = head;
			q = q->next;
		}
		head = head->next;
	}
	q->next = NULL;
	s->next = r->next;
	delete r;
	return p->next;
    }
};