83. Remove Duplicates from Sorted List (Easy)

https://leetcode.com/problems/remove-duplicates-from-sorted-list/

Given a sorted linked list, delete all duplicates such that each element appear only once.

Example 1:

Input: 1->1->2
Output: 1->2

Example 2:

Input: 1->1->2->3->3
Output: 1->2->3

Solutions

class Solution {
    public ListNode deleteDuplicates(ListNode head) {
        if (head == null) {
            return head;
        }

        // preHead used to link to head and faciliate remove operation
        ListNode preHead = new ListNode(-1);
        preHead.next = head;

        ListNode p1 = head;
        ListNode p2 = head.next;

        while (p2 != null) {
            if (p1.val != p2.val) {
                // different values, move on pointers
                p1 = p2;
                p2 = p2.next;
            } else {
                // same value, remove p2, link p1.next = p2.next; p2 = p1.next
                p1.next = p2.next;
                p2 = p1.next;
            }
        }

        return preHead.next;
    }
}

Incorrect Solutions

References

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