Remove Duplicates from Sorted List刪除有序鏈表中的相同元素

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

題意：如題
解法一：設一個指向當前元素的指針，與後面的元素比較

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode* deleteDuplicates(ListNode* head) {
        ListNode *cur = head;
        while(cur && cur->next){
            if(cur->next->val == cur->val){
                cur->next = cur->next->next;
            }
            else{
                cur = cur->next;
            }
        }
        return head;
    }
};

解法二：遞歸

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