[leetcode 83]Remove Duplicates from Sorted List

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本文介绍如何通过递归和迭代两种方式删除排序链表中出现多次的元素，确保每个元素只出现一次。

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.

递归

/**
 * 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 || !head->next) {
            return head;
        }
        ListNode dummy(head->val + 1);
        dummy.next = head;
        recur(&dummy,head);
        return dummy.next;
    }
    void recur(ListNode *prev, ListNode *cur) {
        if (!cur) {
            return ;
        }
        if (prev->val == cur->val) {
            prev->next = cur->next;
            delete cur;
            recur(prev, prev->next);
        } else {
            recur(prev->next, cur->next);
        }
    }
};

迭代

/**
 * 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 || !head->next) {
            return head;
        }
        ListNode dummy(head->val + 1);
        dummy.next = head;
        auto prev = &dummy;
        auto cur = head;
        while (cur) {
            if (prev->val == cur->val) {
                prev->next = cur->next;
                delete cur;
                cur = prev->next;
            } else {
                prev->next = cur;
                prev = cur;
                cur = cur->next;
            }
        }
        return head;
    }
};