LeetCode 83 remove sorts the list pointer speed recursively repeating elements

Title Description

Given a sorted list, delete all the duplicate elements, so that each element occurs only once.

Example 1:

输入: 1->1->2
输出: 1->2

Example 2:

输入: 1->1->2->3->3
输出: 1->2->3

analysis

Speed ​​pointer may be used to cover the element repeats, can also be covered using a recursive method.

Code

Pointer speed

class Solution {
public:
    ListNode* deleteDuplicates(ListNode* head) {
        if (!head || !head -> next) return head;
        ListNode* p = head;
        ListNode* q = head -> next;
        while (p -> next != NULL && p != NULL)
            if (p->val == q -> val) {
                p -> next = q ->next;
                q = q -> next;
            }
            else {
                p = p -> next;
                q = q -> next;
            }
    }
};

Recursion

class Solution {
public:
    ListNode* deleteDuplicates(ListNode* head) {
        if (!head || !head -> next) return head;
        head -> next = deleteDuplicates(head -> next);
        if (head -> next -> val == head ->val) head = head -> next;
        return head;
    }
};