LeetCode - Remove Duplicates from Sorted List

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;
}
};