86. Partition List (注意p2->next = NULL)

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小于x的挂载在p1,其他的挂载在p2
要注意！！！！p2->next = NULL!!!!否则会报错，因为是以NULL为末尾检测！！！

/**
 * 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) {
        ListNode *dummy1 = new ListNode(0);
        ListNode *dummy2 = new ListNode(0);
        ListNode *p = head, *p1 = dummy1,*p2 = dummy2;
        while(p){
            cout<val<val < x){
                p1->next = p;
                p = p->next;
                p1 = p1->next;
            }
            else{
                p2->next = p;
                p = p->next;
                p2 = p2->next;
            }
        }
        p2->next = NULL;
        p1->next = dummy2->next;
        return dummy1->next;
    }
};