Partition List

Given a linked list and a value x, partition it such that all nodes less than x come before nodes greater than or equal to x.

You should preserve the original relative order of the nodes in each of the two partitions.

For example,
Given 1->4->3->2->5->2 and x = 3,
return 1->2->2->4->3->5.

/**
 * 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) {
        if(head == NULL) return NULL;
        ListNode *small, *big, *shead, *bhead;
        shead = (ListNode *)malloc(sizeof(ListNode));
        bhead = (ListNode *)malloc(sizeof(ListNode));
        shead->next = bhead->next = NULL;
        small = shead;
        big = bhead;
        while(head != NULL){
            if(head->val >= x){
                ListNode *tmp = (ListNode *)malloc(sizeof(ListNode));
                tmp->val = head->val;
                tmp->next = NULL;
                big->next = tmp;
                big = tmp;
            }
            else {
                ListNode *tmp = (ListNode *)malloc(sizeof(ListNode));
                tmp->val = head->val;
                tmp->next = NULL;
                small->next = tmp;
                small = tmp;
            }
            head = head->next;
        }
        small->next = bhead->next;
        return shead->next;
    }
};