[LeetCode] 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.

思路一：

/**
 * 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;
        
        for (ListNode *prev = head; prev->next != NULL;) {
            ListNode *q = prev->next;
            if (prev->val == q->val) {
                prev->next = q->next;
                delete q;
            } else {
                prev = prev->next;
            }
        }
        
        return head;
    }
};

思路二：纯粹是练习二级指针的用法，和第一种没有太大区别

/**
 * 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;
        
      for (ListNode **curr = &head; (*curr)->next != NULL; ) {
          ListNode *q = (*curr)->next;
          if ((*curr)->val == q->val) {
              (*curr)->next = q->next;
              delete q;
          } else {
              curr = &((*curr)->next);
          }
      }
      
      return head;
    }
};