LeetCode刷题笔录Remove Duplicates From Sorted List

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

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

先写了一个用extra space的方法，

public class Solution {
    public ListNode deleteDuplicates(ListNode head) {
        if(head == null)
            return null;
        ListNode newHead = new ListNode(head.val);
        ListNode previous = newHead;
        ListNode node = head;
        while(node.next != null){
            node = node.next;
            if(node.val == previous.val)
                continue;
            else{
                ListNode newNode = new ListNode(node.val);
                previous.next = newNode;
                previous = newNode;
            }
        }
        return newHead;
    }
}

再写一个不用extra space的方法，注意如果node.val==node.next.val的话，node.next = node.next.next，此时只改node.next，node本身不前进。

public class Solution {
    public ListNode deleteDuplicates(ListNode head) {
        if(head == null)
            return null;
        ListNode node = head;
        while(node.next != null){
            if(node.val == node.next.val){
                node.next = node.next.next;
            }
            else{
                node = node.next;
            }
        }
        return head;
    }
}