LEETCODE: 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) {        if(head == NULL || head->next == NULL)  return head;        ListNode *pre = head;        ListNode *cur = head->next;        while(cur != NULL) {            if(pre->val == cur->val) {                pre->next = cur->next;            }            else {                pre = cur;            }            cur = cur->next;        }        return head;    }};