Remove Duplicates from Sorted List II

1. Problem Description

Given the head head of a sorted linked list, delete all nodes whose values are duplicated, leaving only values that appear once. Return the sorted linked list.

2. Approach

Compared with Remove Duplicates from Sorted List, this adds an if/else branch.

3. Implementation

/**
 * Definition for singly-linked list.
 * type ListNode struct {
 *     Val int
 *     Next *ListNode
 * }
 */
func deleteDuplicates(head *ListNode) *ListNode {
    if head == nil || head.Next == nil {
        return head
    }
    dummyHead := &ListNode{}
    d := dummyHead
    current := head
    for current != nil {
        next := current.Next
        current.Next = nil

        if next != nil && current.Val == next.Val {
            for next != nil && current.Val == next.Val {
                next = next.Next
            }
        } else {
            d.Next = current
            d = d.Next
        }
        
        current = next
    }
    return dummyHead.Next
}

4. References

• 82. Remove Duplicates from Sorted List II - LeetCode