Remove Duplicates from Sorted List-LeetCode#83

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

删除链表中的重复项
给定已排序的链接列表，删除所有重复项，使每个元素只出现一次。
递归，当 head.val 与 head.next.val 相等时，return head.next；

public class RemoveDuplicatesFromSortedListII {
    public ListNode deleteDuplicates(ListNode head) {
        if (head == null) return null;
        return dfs(head);
    }
    public ListNode dfs(ListNode head){
        if (head.next == null) return head;
        if (head.val == head.next.val){
            return dfs(head.next);
        }else {
            head.next = dfs(head.next);
            return head;
        }
    }
    public static void main(String[] args) {
        RemoveDuplicatesFromSortedListII removeDuplicatesFromSortedListII = new RemoveDuplicatesFromSortedListII();
        ListNode l1 = new ListNode(1);
        l1.next = new ListNode(1);
        l1.next.next = new ListNode(1);
        l1.next.next.next = new ListNode(2);
        l1.next.next.next.next = new ListNode(3);
        removeDuplicatesFromSortedListII.deleteDuplicates(l1);
    }
}