# Question

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
```

# Solution

```
# Definition for singly-linked list.
# class ListNode:
# def __init__(self, x):
# self.val = x
# self.next = None
class Solution:
def deleteDuplicates(self, head):
"""
:type head: ListNode
:rtype: ListNode
"""
if head is None or head.next is None:
return head
prev = head
curr = head.next
value = prev.val
while curr is not None:
if curr.val != value:
prev.next = curr
prev = curr
value = curr.val
curr = curr.next
prev.next = None
return head
```