# 83 Remove Duplicates from Sorted List

## 83. [Remove Duplicates from Sorted List](https://leetcode.com/problems/remove-duplicates-from-sorted-list/description/)

## 1. Question

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

For example,\
Given`1->1->2`, return`1->2`.\
Given`1->1->2->3->3`, return`1->2->3`.

## 2. Implementation

```java
/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public ListNode deleteDuplicates(ListNode head) {
        if (head == null) {
            return head;
        }

        ListNode preNode = head, curNode = head.next;
        while (curNode != null) {
            if (preNode.val == curNode.val) {
                preNode.next = curNode.next;
            }
            else {
                preNode = preNode.next;
            }
            curNode = curNode.next;
        }
        return head;
    }
}
```

## 3. Time & Space Complexity

时间复杂度O(n), 空间复杂度O(1)