[Swift 4] Update Skip List

Author: remlostime

Skip-List/SkipList.playground/Contents.swift

@@ -0,0 +1,7 @@
+// last checked with Xcode 9.0b4
+#if swift(>=4.0)
+print("Hello, Swift 4!")
+#endif
+
+// SkipList is ready for Swift 4.
+// TODO: Add Test

Skip-List/SkipList.playground/Sources/SkipList.swift

@@ -0,0 +1,270 @@
+// The MIT License (MIT)
+
+// Copyright (c) 2016 Mike Taghavi (mitghi[at]me.com)
+
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+import Foundation
+
+// Stack from : https://github.com/raywenderlich/swift-algorithm-club/tree/master/Stack
+public struct Stack<T> {
+  fileprivate var array: [T] = []
+
+  public var isEmpty: Bool {
+    return array.isEmpty
+  }
+
+  public var count: Int {
+    return array.count
+  }
+
+  public mutating func push(_ element: T) {
+    array.append(element)
+  }
+
+  public mutating func pop() -> T? {
+    return array.popLast()
+  }
+
+  public func peek() -> T? {
+    return array.last
+  }
+}
+
+extension Stack: Sequence {
+  public func makeIterator() -> AnyIterator<T> {
+    var curr = self
+    return AnyIterator { curr.pop() }
+  }
+}
+
+private func coinFlip() -> Bool {
+  return arc4random_uniform(2) == 1
+}
+
+public class DataNode<Key: Comparable, Payload> {
+  public typealias Node = DataNode<Key, Payload>
+
+  var data: Payload?
+  fileprivate var key: Key?
+  var next: Node?
+  var down: Node?
+
+  public init(key: Key, data: Payload) {
+    self.key  = key
+    self.data = data
+  }
+
+  public init(asHead head: Bool) {}
+
+}
+
+open class SkipList<Key: Comparable, Payload> {
+  public typealias Node = DataNode<Key, Payload>
+
+  fileprivate(set) var head: Node?
+
+  public init() {}
+
+}
+
+// MARK: - Search lanes for a node with a given key
+
+extension SkipList {
+
+  func findNode(key: Key) -> Node? {
+    var currentNode: Node? = head
+    var isFound: Bool = false
+
+    while !isFound {
+      if let node = currentNode {
+
+        switch node.next {
+        case .none:
+
+          currentNode = node.down
+        case .some(let value) where value.key != nil:
+
+          if value.key == key {
+            isFound = true
+            break
+          } else {
+            if key < value.key! {
+              currentNode = node.down
+            } else {
+              currentNode = node.next
+            }
+          }
+
+        default:
+          continue
+        }
+
+      } else {
+        break
+      }
+    }
+
+    if isFound {
+      return currentNode
+    } else {
+      return nil
+    }
+
+  }
+
+  func search(key: Key) -> Payload? {
+    guard let node = findNode(key: key) else {
+      return nil
+    }
+
+    return node.next!.data
+  }
+
+}
+
+// MARK: - Insert a node into lanes depending on skip list status ( bootstrap base-layer if head is empty / start insertion from current head ).
+
+extension SkipList {
+  private func bootstrapBaseLayer(key: Key, data: Payload) {
+    head       = Node(asHead: true)
+    var node   = Node(key: key, data: data)
+
+    head!.next = node
+
+    var currentTopNode = node
+
+    while coinFlip() {
+      let newHead    = Node(asHead: true)
+      node           = Node(key: key, data: data)
+      node.down      = currentTopNode
+      newHead.next   = node
+      newHead.down   = head
+      head           = newHead
+      currentTopNode = node
+    }
+
+  }
+
+  private func insertItem(key: Key, data: Payload) {
+    var stack              = Stack<Node>()
+    var currentNode: Node? = head
+
+    while currentNode != nil {
+
+      if let nextNode = currentNode!.next {
+        if nextNode.key! > key {
+          stack.push(currentNode!)
+          currentNode = currentNode!.down
+        } else {
+          currentNode = nextNode
+        }
+
+      } else {
+        stack.push(currentNode!)
+        currentNode = currentNode!.down
+      }
+
+    }
+
+    let itemAtLayer    = stack.pop()
+    var node           = Node(key: key, data: data)
+    node.next          = itemAtLayer!.next
+    itemAtLayer!.next  = node
+    var currentTopNode = node
+
+    while coinFlip() {
+      if stack.isEmpty {
+        let newHead    = Node(asHead: true)
+
+        node           = Node(key: key, data: data)
+        node.down      = currentTopNode
+        newHead.next   = node
+        newHead.down   = head
+        head           = newHead
+        currentTopNode = node
+
+      } else {
+        let nextNode  = stack.pop()
+
+        node           = Node(key: key, data: data)
+        node.down      = currentTopNode
+        node.next      = nextNode!.next
+        nextNode!.next = node
+        currentTopNode = node
+      }
+    }
+  }
+
+  func insert(key: Key, data: Payload) {
+    if head != nil {
+      if let node = findNode(key: key) {
+        // replace, in case of key already exists.
+        var currentNode = node.next
+        while currentNode != nil && currentNode!.key == key {
+          currentNode!.data = data
+          currentNode       = currentNode!.down
+        }
+      } else {
+        insertItem(key: key, data: data)
+      }
+
+    } else {
+      bootstrapBaseLayer(key: key, data: data)
+    }
+  }
+
+}
+
+// MARK: - Remove a node with a given key. First, find its position in layers at the top, then remove it from each lane by traversing down to the base layer.
+
+extension SkipList {
+  public func remove(key: Key) {
+    guard let item = findNode(key: key) else {
+      return
+    }
+
+    var currentNode = Optional(item)
+
+    while currentNode != nil {
+      let node   = currentNode!.next
+
+      if node!.key != key {
+        currentNode = node
+        continue
+      }
+
+      let nextNode      = node!.next
+
+      currentNode!.next = nextNode
+      currentNode       = currentNode!.down
+
+    }
+
+  }
+}
+
+// MARK: - Get associated payload from a node with a given key.
+
+extension SkipList {
+
+  public func get(key: Key) -> Payload? {
+    return search(key: key)
+  }
+}

Skip-List/SkipList.playground/contents.xcplayground

@@ -0,0 +1,4 @@
+<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
+<playground version='5.0' target-platform='ios'>
+    <timeline fileName='timeline.xctimeline'/>
+</playground>

Skip-List/SkipList.playground/playground.xcworkspace/contents.xcworkspacedata

@@ -50,18 +50,12 @@ public struct Stack<T> {
 extension Stack: Sequence {
   public func makeIterator() -> AnyIterator<T> {
     var curr = self
-    return AnyIterator { _ -> T? in
-      return curr.pop()
-    }
+    return AnyIterator { curr.pop() }
   }
 }
 
 private func coinFlip() -> Bool {
-  #if os(Linux)
-      return random() % 2 == 0
-  #elseif os(OSX)
-      return arc4random_uniform(2) == 1
-  #endif
+  return arc4random_uniform(2) == 1
 }
 
 public class DataNode<Key: Comparable, Payload> {
@@ -221,7 +215,7 @@ extension SkipList {
   func insert(key: Key, data: Payload) {
     if head != nil {
       if let node = findNode(key: key) {
-        // replace, in case of key already exists. 
+        // replace, in case of key already exists.
         var currentNode = node.next
         while currentNode != nil && currentNode!.key == key {
           currentNode!.data = data
@@ -274,3 +268,4 @@ extension SkipList {
     return search(key: key)
   }
 }
+