[leetcode]Partition List

/**
* 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) {
// Start typing your C/C++ solution below
// DO NOT write int main() function
if(!head) return NULL;

ListNode *lt = new ListNode(0);
lt->next = head;
ListNode *gt = new ListNode(0);

ListNode *p = lt, *q = gt;

while(p->next){
if(p->next->val >= x){
q->next = p->next;
p->next = q->next->next;
q = q->next;
q->next = NULL;

}else{
p = p->next;
}
}

p->next = gt->next;
head = lt->next;

delete lt;
delete gt;

return head;
}
};