83. Remove Duplicates from Sorted List

难度：easy
问题描述：
Given a sorted linked list, delete all duplicates such that each element appear only once.
中文：移除重复的节点
Example 1:

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

Example 2:

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

解法1：

简单暴力的遍历，注意判断空链表：

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */

ListNode* deleteDuplicates(ListNode* head) {
        if(head == nullptr) return nullptr;
        ListNode* h = head;
        while(head->next != nullptr){
            if(head ->val != head->next->val){
                head = head->next;
            }else{
                head->next = head->next->next;
            }
        }
        return h;
    }

解法2：

递归法，判断前一个是否和后一个相等，如果相等则返回后一个。

ListNode* deleteDuplicates(ListNode* head) {
	if (!head || !head->next) return head;
		head->next = deleteDuplicates(head->next);
	return (head->val == head->next->val) ? head->next : head;
}