83 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.

Solution

/**
 * 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 ) return head;
        ListNode *p1 = head, *p2 = head->next;
        while ( p2 != NULL ) {
            if ( p1->val == p2->val ) p1->next = p2->next;
            else p1 = p2;
            p2 = p1->next;
        }
        return head;
    }
};