[leetcode] 83 Remove Duplicates from Sorted List C++

/*
http://leetcode.com/onlinejudge#question_83

Given a sorted linked list, delete all duplicates such that each element appear only once.

For example,
Given 1->1->2, return 1->2.
Given 1->1->2->3->3, return 1->2->3.

*/

class Solution {
public:
    ListNode *deleteDuplicates(ListNode *head) {

        ListNode * a = head, *b;

        for(; a != NULL; a = a->next)
        {
            while(NULL != (b = a->next) && a->val == b->val)
            {
                a->next = b->next;
            }
        }
        return head;

    }
};