[Swift]LeetCode203. 移除链表元素 | Remove Linked List Elements

★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★
➤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/10184259.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！
★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★

Remove all elements from a linked list of integers that have value val.

Example:

Input:  1->2->6->3->4->5->6, val = 6
Output: 1->2->3->4->5

---

删除链表中等于给定值 val 的所有节点。

示例:

输入: 1->2->6->3->4->5->6, val = 6
输出: 1->2->3->4->5

---

72ms

/**
 * 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 removeElements(_ head: ListNode?, _ val: Int) -> ListNode? {
        guard head != nil else { return nil }
        
        var head = head
        while head != nil, head!.val == val {
            head = head?.next
        }
        
        var prev = head
        var current = head?.next
        
        while let curr = current {
            if curr.val == val {
                prev?.next = curr.next
                current = curr.next
                continue
            }
            prev = curr
            current = curr.next
        }
        
        return head
    }
}

---

76ms

/**
 * 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 removeElements(_ head: ListNode?, _ val: Int) -> ListNode? {
        guard let head = head else { return nil }
        head.next = removeElements(head.next, val)
        return head.val == val ? head.next : head
    }
}

---

80ms

/**
 * 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 removeElements(_ head: ListNode?, _ val: Int) -> ListNode? {

        var dummy = ListNode(-1)
        dummy.next = head
        var cur = dummy
        while cur.next != nil {
            if cur.next!.val == val {
                cur.next = cur.next!.next
            }
            else{
                cur = cur.next!
            }
        }
        return dummy.next
    }
}

---

96ms

/**
 * 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 removeElements(_ head: ListNode?, _ val: Int) -> ListNode? {
        guard let _ = head else {
            return nil
        }
        
        //在表头添加一个哨兵节点
        let fakeNode = ListNode(NSNotFound)
        fakeNode.next = head
        var prev:ListNode = fakeNode
        var current:ListNode? = head
        while let tmp = current {
            if tmp.val != val {
                prev.next = tmp
                prev = prev.next!
            }
            current = tmp.next
        }
        
        if prev.next != nil {
            prev.next = nil
        }
        return fakeNode.next
    }
}