82. Remove Duplicates from Sorted List II

problem description

Given a sorted linked list, delete all nodes that have duplicate numbers, leaving only distinct numbers from the original list.

Example 1:

Input: 1->2->3->3->4->4->5
Output: 1->2->5

Example 2:

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

algorithm thought

又是链表问题，并且直接返回一个链表。和之前做链表题一样直接用递归的形式解决

code

/**
 * 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)
            return NULL;
        ListNode* now=head;
        head=head->next;
        if(head&&head->val==now->val){
            while(head&&head->val==now->val)
                head=head->next;
            return deleteDuplicates(head);
        }else{
            now->next=deleteDuplicates(head);
            return now;
        }
    }
};

algorithm analysis

一次遍历解决，时间复杂度O(n)