链表划分-LintCode

给定一个单链表和数值x，划分链表使得所有小于x的节点排在大于等于x的节点之前。
你应该保留两部分内链表节点原有的相对顺序。
样例:
给定链表 1->4->3->2->5->2->null，并且 x=3
返回 1->2->2->4->3->5->null

#ifndef C96_H#define C96_H#include<iostream>using namespace std;class ListNode{public:    int val;    ListNode *next;    ListNode(int val)    {        this->val = val;        this->next = NULL;    }};class Solution {public:    /**    * @param head: The first node of linked list.    * @param x: an integer    * @return: a ListNode    */    ListNode *partition(ListNode *head, int x) {        // write your code here        ListNode *p = head, *preHead=new ListNode(0), *postHead=new ListNode(0);        ListNode *pre = preHead, *post = postHead;        while (p != NULL)        {            ListNode *next = p->next;            if (p->val >= x)            {                post->next=p;                post = post->next;                post->next = NULL;            }            else            {                pre->next = p;                pre = pre->next;                pre->next = NULL;            }            p = next;        }        pre->next = postHead->next;        return preHead->next;    }};#endif