leetcode 37: Remove Duplicates from Sorted List

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.

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode *deleteDuplicates(ListNode *head) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        if( head == NULL) return head;
        int temp = head->val;
        ListNode * cur = head->next;
        ListNode * pre = head;
        
        while( cur!=NULL ) {
            if( cur->val != temp) {
                temp = cur->val;                
                pre = cur;
                
            } else {
                pre->next = cur->next;
            }
            cur = cur->next;
        }
        return head;
    }
};