30：Remove Duplicates from Sorted List

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题目：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.

解题代码版本一：

//迭代版本//时间复杂度O(n)，空间复杂度O(1)class Solution {public:        ListNode* deleteDuplicates(ListNode* head) {                if (head == nullptr) return head;                ListNode* prev = head;                ListNode* cur = head -> next;                while (cur != nullptr) {                        if (cur -> val == prev -> val) {                                prev -> next = cur -> next;                                delete cur;                                cur = prev -> next;                        }                        else {                                prev = prev -> next;                                cur = cur -> next;                        }                }                return cur;        }};

解题代码版本二：

/递归版本//时间复杂度O(n)，空间复杂度O(1)class Solution {public:        ListNode* deleteDuplicates(ListNode* head) {                if (head == nullptr || head -> next == nullptr)                        return head;                ListNode* p = head -> next;                if (p -> val == head -> val) {                        while (p && head -> val == p -> val) {                                auto tmp = p;                                p = p -> next;                                delete tmp;                        }                }                head -> next = deleteDuplicates(p);                return head;        }};

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