[Swift]LeetCode83. 删除排序链表中的重复元素 | Remove Duplicates from Sorted List

★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★
➤微信公众号：山青咏芝（shanqingyongzhi）
➤博客园地址：山青咏芝（https://www.cnblogs.com/strengthen/）
➤GitHub地址：https://github.com/strengthen/LeetCode
➤原文地址：https://www.cnblogs.com/strengthen/p/9697982.html 
➤如果链接不是山青咏芝的博客园地址，则可能是爬取作者的文章。
➤原文已修改更新！强烈建议点击原文地址阅读！支持作者！支持原创！
★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★

Given a sorted linked list, delete all duplicates such that each element appear only once.

Example 1:

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

Example 2:

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

---

给定一个排序链表，删除所有重复的元素，使得每个元素只出现一次。

示例 1:

输入: 1->1->2
输出: 1->2

示例 2:

输入: 1->1->2->3->3
输出: 1->2->3

---

28ms

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     public var val: Int
 *     public var next: ListNode?
 *     public init(_ val: Int) {
 *         self.val = val
 *         self.next = nil
 *     }
 * }
 */
class Solution {
    func deleteDuplicates(_ head: ListNode?) -> ListNode? {
        var temp = head
        while temp != nil {
            if temp?.next?.val == temp?.val {
                temp?.next = temp?.next?.next
            } else {
               temp = temp?.next 
            }
        }
        
        return head
    }
}

---

32ms

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     public var val: Int
 *     public var next: ListNode?
 *     public init(_ val: Int) {
 *         self.val = val
 *         self.next = nil
 *     }
 * }
 */
class Solution {
    func deleteDuplicates(_ head: ListNode?) -> ListNode? {
        
        var node: ListNode? = head
        var next: ListNode? = nil
        
        while node != nil {
            
            next = node!.next
            while next != nil && next!.val == node!.val {
                next = next!.next
            }
            
            node!.next = next
            node = next
        }
        
        return head
    }
}

---

60ms

class Solution {
    func deleteDuplicates(_ head: ListNode?) -> ListNode? {
        var r = head
        while r?.next != nil {
            if r?.val == r?.next?.val {
                r?.next = r?.next?.next
            } else {
                r = r?.next
            }
        }
        return head
    }
}

---

64ms

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     public var val: Int
 *     public var next: ListNode?
 *     public init(_ val: Int) {
 *         self.val = val
 *         self.next = nil
 *     }
 * }
 */
class Solution {
    
    func deleteDuplicates(_ head: ListNode?) -> ListNode? {
        guard var head = head else{
            return nil
        }
        
        func remove(_ current:ListNode, _ previous:ListNode? = nil) {
            guard let pre = previous else{
                if current.next != nil {
                    remove(current.next!,current)
                }
                return
            }
            if pre.val == current.val {
                pre.next = current.next
                if current.next != nil {
                    remove(current.next!,pre)
                }
                return
            }else{
                if current.next != nil {
                    remove(current.next!,current)
                }
            }
        }
        
        remove(head)
        return head
    }
    
}