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LinkedList.swift
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LinkedList.swift
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//
// LinkedList.swift
// SwiftAlgorithm
//
// Created by Lee Myeonghwan on 2023/02/08.
//
import Foundation
struct LinkedList<T>: CustomStringConvertible {
class Node<T>: CustomStringConvertible, Equatable {
var value: T
var next: Node?
var description: String {
guard let next = next else { return "\(value)" }
return "\(value) -> " + String(describing: next)
}
init(value: T, next: Node? = nil) {
self.value = value
self.next = next
}
static func ==(lhs: Node, rhs: Node) -> Bool {
return lhs.next == rhs.next
}
}
var head: Node<T>?
var tail: Node<T>?
init() { }
var isEmpty: Bool {
return head == nil
}
var description: String {
guard let head = head else { return "Empty list" }
return String(describing: head)
}
}
// common operations
extension LinkedList {
func node(at index: Int) -> Node<T>? {
if isEmpty {
return nil
}
var currentNode = head
var currentIndex = 0
while currentNode != nil && currentIndex < index {
currentNode = currentNode?.next
currentIndex += 1
}
return currentNode
}
func numberOfNodes() -> Int {
var currentNode = head
var count = 0
while currentNode != nil {
currentNode = currentNode?.next
count += 1
}
return count
}
// 이 메소드 이후 메모리상에서 해제되었는지 확인 가능?
mutating func removeAll() {
head = nil
tail = nil
}
}
// insertion operations
extension LinkedList {
subscript(index: Int) -> Node<T>? {
node(at: index)
}
mutating func push(_ value: T) {
let newNode = Node(value: value, next: head)
head = newNode
if tail == nil {
tail = head
}
}
mutating func append(_ value: T) {
if isEmpty {
self.push(value)
return
}
tail?.next = Node(value: value)
tail = tail?.next
}
mutating func insert(_ value: T, after index: Int) {
if index < 0 || index >= self.numberOfNodes() {
self.append(value)
return
}
if let beforeNode = self.node(at: index), let tail = tail {
if beforeNode == tail {
self.append(value)
} else {
beforeNode.next = Node(value: value, next: beforeNode.next)
}
} else {
self.push(value)
}
}
}
// deletion operations
extension LinkedList {
@discardableResult
mutating func pop() -> T? {
defer {
head = head?.next
if isEmpty {
tail = nil
}
}
return head?.value
}
@discardableResult
mutating func deleteLast() -> T? {
guard let head = head else { return nil }
guard head.next != nil else { return pop() }
var currentNode = head
var previousNode = head
while let next = currentNode.next {
previousNode = currentNode
currentNode = next
}
previousNode.next = nil
tail = previousNode
return currentNode.value
}
mutating func remove(after index: Int) -> T? {
if index < 0 || index >= self.numberOfNodes() {
return nil
}
if let beforeNode = self.node(at: index) {
defer {
if beforeNode.next == tail {
tail = beforeNode
}
beforeNode.next = beforeNode.next?.next
}
return beforeNode.next?.value
}
return nil
}
}