[Swift]LeetCode707. 设计链表 | Design Linked 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/10506371.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！
★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★

Design your implementation of the linked list. You can choose to use the singly linked list or the doubly linked list. A node in a singly linked list should have two attributes: val and next. valis the value of the current node, and next is a pointer/reference to the next node. If you want to use the doubly linked list, you will need one more attribute prev to indicate the previous node in the linked list. Assume all nodes in the linked list are 0-indexed.

Implement these functions in your linked list class:

• get(index) : Get the value of the index-th node in the linked list. If the index is invalid, return -1.
• addAtHead(val) : Add a node of value val before the first element of the linked list. After the insertion, the new node will be the first node of the linked list.
• addAtTail(val) : Append a node of value val to the last element of the linked list.
• addAtIndex(index, val) : Add a node of value val before the index-th node in the linked list. If index equals to the length of linked list, the node will be appended to the end of linked list. If index is greater than the length, the node will not be inserted.
• deleteAtIndex(index) : Delete the index-th node in the linked list, if the index is valid.

Example:

MyLinkedList linkedList = new MyLinkedList();
linkedList.addAtHead(1);
linkedList.addAtTail(3);
linkedList.addAtIndex(1, 2);  // linked list becomes 1->2->3
linkedList.get(1);            // returns 2
linkedList.deleteAtIndex(1);  // now the linked list is 1->3
linkedList.get(1);            // returns 3

Note:

• All values will be in the range of [1, 1000].
• The number of operations will be in the range of [1, 1000].
• Please do not use the built-in LinkedList library.

---

设计链表的实现。您可以选择使用单链表或双链表。单链表中的节点应该具有两个属性：val 和 next。val 是当前节点的值，next 是指向下一个节点的指针/引用。如果要使用双向链表，则还需要一个属性 prev 以指示链表中的上一个节点。假设链表中的所有节点都是 0-index 的。

在链表类中实现这些功能：

• get(index)：获取链表中第 index 个节点的值。如果索引无效，则返回-1。
• addAtHead(val)：在链表的第一个元素之前添加一个值为 val 的节点。插入后，新节点将成为链表的第一个节点。
• addAtTail(val)：将值为 val 的节点追加到链表的最后一个元素。
• addAtIndex(index,val)：在链表中的第 index 个节点之前添加值为 val  的节点。如果 index 等于链表的长度，则该节点将附加到链表的末尾。如果 index 大于链表长度，则不会插入节点。
• deleteAtIndex(index)：如果索引 index 有效，则删除链表中的第 index 个节点。

示例：

MyLinkedList linkedList = new MyLinkedList();
linkedList.addAtHead(1);
linkedList.addAtTail(3);
linkedList.addAtIndex(1,2);   //链表变为1-> 2-> 3
linkedList.get(1);            //返回2
linkedList.deleteAtIndex(1);  //现在链表是1-> 3
linkedList.get(1);            //返回3

提示：

• 所有值都在 [1, 1000] 之内。
• 操作次数将在  [1, 1000] 之内。
• 请不要使用内置的 LinkedList 库。

---

Runtime: 168 ms

Memory Usage: 19.3 MB

class MyLinkedList {
    var list:[Int] = [Int].init()
    /** Initialize your data structure here. */
    init() {
        
    }
    
    /** Get the value of the index-th node in the linked list. If the index is invalid, return -1. */
    func get(_ index: Int) -> Int {
       if list.count > index {
           return list[index]
       }
        return -1
    }
    
    /** Add a node of value val before the first element of the linked list. After the insertion, the new node will be the first node of the linked list. */
    func addAtHead(_ val: Int) {
        if list.count > 0 {
            list.insert(val,at:0)
        } else {
            list.append(val)
        }
    }
    
    /** Append a node of value val to the last element of the linked list. */
    func addAtTail(_ val: Int) {
        list.append(val)
    }
    
    /** Add a node of value val before the index-th node in the linked list. If index equals to the length of linked list, the node will be appended to the end of linked list. If index is greater than the length, the node will not be inserted. */
    func addAtIndex(_ index: Int, _ val: Int) {
        if list.count > index {
            list.insert(val,at:index)
        } else if list.count == index {
            list.append(val)
        }
    }
    
    /** Delete the index-th node in the linked list, if the index is valid. */
    func deleteAtIndex(_ index: Int) {
        if list.count > index {
            list.remove(at:index)
        }
    }
}

/**
 * Your MyLinkedList object will be instantiated and called as such:
 * let obj = MyLinkedList()
 * let ret_1: Int = obj.get(index)
 * obj.addAtHead(val)
 * obj.addAtTail(val)
 * obj.addAtIndex(index, val)
 * obj.deleteAtIndex(index)
 */

---

196ms

class MyLinkedList {
 
    var list = [Int]()

    /** Initialize your data structure here. */
    init() {
           
    }
    
    /** Get the value of the index-th node in the linked list. If the index is invalid, return -1. */
    func get(_ index: Int) -> Int {
      if index < list.count {
          return list[index]
      }

      return -1
    }
    
    /** Add a node of value val before the first element of the linked list. After the insertion, the new node will be the first node of the linked list. */
    func addAtHead(_ val: Int) {
      list.insert(val, at: 0)
    }
    
    /** Append a node of value val to the last element of the linked list. */
    func addAtTail(_ val: Int) {
      list.append(val)
    }
    
    /** Add a node of value val before the index-th node in the linked list. If index equals to the length of linked list, the node will be appended to the end of linked list. If index is greater than the length, the node will not be inserted. */
     func addAtIndex(_ index: Int, _ val: Int) {
        if index <= list.count {
            list.insert(val, at: index)
        }
    }
    
    /** Delete the index-th node in the linked list, if the index is valid. */
    func deleteAtIndex(_ index: Int) {
      if index < list.count {
          list.remove(at: index)
      }
    }
}

---

216ms

class MyLinkedList {

    private var count: Int = 0
    private var head: Node? = nil
    private var tail: Node? = nil
    
    init() {
        
    }
    
    public func get(_ index: Int) -> Int {
        return _get(index)?.val ?? -1
    }
    
    private func _get(_ index: Int) -> Node? {
        var curr = head
        
        for _ in 0..<index {
            curr = curr?.next
        }
        
        return curr
    }
    
    public func addAtHead(_ val: Int) {
        let node = Node()
        node.val = val
        
        if head == nil {
            head = node
            tail = node
        } else {
            node.next = head
            head?.prev = node
            head? = node
        }
        
        count += 1
    }
    
    public func addAtTail(_ val: Int) {
        let node = Node()
        node.val = val
        
        if head == nil {
            head = node
            tail = node
        } else {
            node.prev = tail
            tail?.next = node
            tail = node
        }
        
        count += 1
    }
    
    public func addAtIndex(_ index: Int, _ val: Int) {
        guard index <= count else { return }
        if index == 0 {
            addAtHead(val)
        } else if index >= count {
            addAtTail(val)
        } else {
            let node = _get(index - 1)
            let new = Node()
            new.val = val
            
            new.next = node?.next
            new.next?.prev = new
            new.prev = node
            node?.next = new
            
            count += 1
        }
    }
    
    public func deleteAtIndex(_ index: Int) {
        guard index < count else { return }
        if index == 0 {
            let node = head!
            if tail === node {
                tail = nil
            }
            head = node.next
            head?.prev = nil
            node.next = nil
        } else if index >= count - 1 {
            let node = tail!
            tail = tail?.prev
            tail?.next = nil
            node.prev = nil
        } else {
            let node = _get(index)
            node?.prev?.next = node?.next
            node?.next?.prev = node?.prev
        }
        count -= 1
    }
    
    private class Node {
        var val: Int = 0
        var next: Node? = nil
        var prev: Node? = nil
    }
}

---

224ms

class MyLinkedList {
    
    private class Node {
        var next: Node?
        var prev: Node?
        var val: Int
        
        init(_ val: Int, next: Node? = nil, prev: Node? = nil) {
            self.val = val
            self.next = next
            self.prev = prev
        }
    }
    
    private var head: Node?
    private var tail: Node?
    var count = 0
    var isEmpty: Bool {
        return count == 0
    }
    
    /** Initialize your data structure here. */
    init() {
        
    }
    
    /** Get the value of the index-th node in the linked list. If the index is invalid, return -1. */
    func get(_ index: Int) -> Int {
        guard index >= 0, index < self.count else {return -1}
        return getNodeForIndex(index).val
    }
    
    /** Add a node of value val before the first element of the linked list. After the insertion, the new node will be the first node of the linked list. */
    func addAtHead(_ val: Int) {
        guard let head = head else {
            self.head = Node(val)
            self.tail = self.head
            self.count += 1
            return
        }
        let newHead = Node(val, next: head, prev: nil)
        head.prev = newHead
        self.head = newHead
        self.count += 1
    }
    
    /** Append a node of value val to the last element of the linked list. */
    func addAtTail(_ val: Int) {
        guard let tail = tail else {
            self.head = Node(val)
            self.tail = self.head
            self.count += 1
            return
        }
        let newTail = Node(val, next: nil, prev: tail)
        tail.next = newTail
        self.tail = newTail
        self.count += 1
    }
    
    /** Add a node of value val before the index-th node in the linked list. If index equals to the length of linked list, the node will be appended to the end of linked list. If index is greater than the length, the node will not be inserted. */
    func addAtIndex(_ index: Int, _ val: Int) {
        guard index >= 0, index <= self.count else { return }
        guard index != 0 else {
            addAtHead(val)
            return
        }
        guard index != self.count else {
            addAtTail(val)
            return
        }
        let current = getNodeForIndex(index - 1)
        let newNode = Node(val, next: current.next, prev: current)
        current.next = newNode
        newNode.next?.prev = newNode
        self.count += 1
    }
    
    /** Delete the index-th node in the linked list, if the index is valid. */
    func deleteAtIndex(_ index: Int) {
        guard index >= 0, index < self.count else { return }
        guard self.count > 1 else {
            self.head = nil
            self.tail = nil
            self.count -= 1
            return
        }
        guard index != 0 else {
            self.head = self.head?.next
            self.head?.prev = nil
            self.count -= 1
            return
        }
        guard index != self.count - 1 else {
            self.tail = self.tail?.prev
            self.tail?.next = nil
            self.count -= 1
            return
        }
        let current = getNodeForIndex(index)
        let prev = current.prev!
        let next = current.next!
        prev.next = next
        next.prev = prev
        self.count -= 1
    }
    
    private func getNodeForIndex(_ index: Int) -> Node {
        if index < self.count / 2 {
            var current = self.head!
            for _ in 0..<index {
                current = current.next!
            }
            return current
        } else {
            var current = self.tail!
            var i = self.count - 1
            while i > index {
                current = current.prev!
                i -= 1
            }
            return current
        }
    }
}

---

328ms

class MyLinkedList {
    
    var head: ListNode?
    var tail: ListNode?
    var size: Int
    
    init(){
        self.size = 0
    }
    
    func get(_ index: Int) -> Int {
        
        if  index >= size {
            return -1;
        }
        
        var tempNode = head
        var i = 0
        while i < index {
            tempNode = tempNode?.next
            i += 1
        }
        
        return tempNode!.val
    }
    
    func addAtHead(_ val: Int){
        
        let node = ListNode(val)
        node.next = head
        head = node
        
        if tail == nil {
            tail = head
        }
        size += 1
    }
    
    func addAtTail(_ val: Int){
        let node = ListNode(val)
        if let tail = tail {
            tail.next = node
         }else {
            head = node
        }
        
        tail = node
        size += 1
        
        
    }
    
    func addAtIndex(_ index:Int, _ val: Int){
        
        if (index > self.size){
            return
        }
        
        if(index == self.size){
            self.addAtTail(val)
            return
        }
        
        if (index == 0) {
            self.addAtTail(val)
            return
        }
        
        
        //需要两个节点--插入位置的前结点，和插入位置的后（现）结点
        //index 位置前面的结点
        var tempNode = head
        var i = 0
        while i < index-1 {
            tempNode = tempNode?.next
            i += 1
        }
        
        let nextNode = tempNode?.next
        
        let node = ListNode(val)
        tempNode?.next = node
        node.next = nextNode
        
        size += 1
    }
    
    func deleteAtIndex(_ index:Int) {
        
        if index >= size {
            return;
        }
        
        if(index == 0){
            if(size == 1){
                size = 0
                head = nil
                tail = nil
            }
            head = head?.next
            size -= 1
            return;
        }
        
        var tempNode = head
        
        for _ in 0..<index-1{
            tempNode = tempNode?.next
        }
        
        if index == size - 1{
            tail = tempNode
            tail?.next = nil
            size -= 1
            return;
        }
        
        let nextNode = tempNode?.next?.next
        tempNode?.next = nextNode
        size -= 1        
    }
}