[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;

    }

};