## Description

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

Given the `head`

of a sorted linked list, *delete all duplicates such that each element appears only once*. Return *the linked list sorted as well*.

**Example 1:**

Input:head = [1,1,2]Output:[1,2]

**Example 2:**

Input:head = [1,1,2,3,3]Output:[1,2,3]

**Constraints:**

- The number of nodes in the list is in the range
`[0, 300]`

. `-100 <= Node.val <= 100`

- The list is guaranteed to be
**sorted**in ascending order.

## Explanation

Have a dictionary to track the visited node values.

## Python Solution

```
# Definition for singly-linked list.
# class ListNode:
# def __init__(self, val=0, next=None):
# self.val = val
# self.next = next
class Solution:
def deleteDuplicates(self, head: ListNode) -> ListNode:
dummy = ListNode(0)
dummy.next = head
visited = set()
while head and head.next:
visited.add(head.val)
while head.next and head.next.val in visited:
head.next = head.next.next
head = head.next
return dummy.next
```

- Time Complexity: O(N).
- Space Complexity: O(N).