83.Remove Duplicates from Sorted List

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Linked List, Easy

Question

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

Example 1:

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

Example 2:

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

Answer

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/**
 * 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 || head.next==null)
            return head;
        ListNode temp = head;
        while(temp!=null&&temp.next!=null){
            if(temp.val == temp.next.val)
                temp.next = temp.next.next;
            else
                temp = temp.next;
        }
        return head;
    }
}

Recursive

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/**
 * 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 || head.next==null)
            return head;
        head.next = deleteDuplicates(head.next);
        return head.val==head.next.val ? head.next : head;
    }
}

Running time: O(n)