LeetCode

Remove Duplicates from Sorted List

2013.12.26 21:36

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:

　　Removing the duplicates from a list requires two pointers ptr1 and ptr2. With ptr1 pointing to current node, and ptr2 next to ptr1, the operation can be done in only one-pass. Please see the code below.

　　Time complexity is O(n), space complexity is O(1).

Accepted code:

/**
 * 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) {
        // Note: The Solution object is instantiated only once and is reused by each test case.
        if(head == nullptr){
            return head;
        }
        
        ListNode *ptr1, *ptr2;

        ptr1 = head;
        ptr2 = head->next;
        while(ptr2 != nullptr){
            if(ptr1->val == ptr2->val){
                ptr1->next = ptr2->next;
                delete ptr2;
                ptr2 = ptr1->next;
            }else{
                ptr1 = ptr1->next;
                ptr2 = ptr1->next;
            }
        }

        return head;
    }
};