leetcode Partition List

class Solution {public:    ListNode* partition(ListNode* head, int x) {        ListNode* smallHead = new ListNode(0);// 增加头结点，简化代码        ListNode* notSmallHead = new ListNode(0);        ListNode* notSmallPtr = notSmallHead;        ListNode* smallPtr = smallHead;        for (ListNode* ptr = head; ptr;){            ListNode* tmp = ptr->next;            if (ptr->val < x){                smallPtr->next = ptr;                smallPtr = ptr;            }            else{                notSmallPtr->next = ptr;                notSmallPtr = ptr;                ptr->next = NULL;            }            ptr = tmp;        }        smallPtr->next = notSmallHead->next;        return smallHead->next;;    }};