122 lines
3 KiB
Swift
122 lines
3 KiB
Swift
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//
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// Heap.swift
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// SwiftHeap
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//
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// Created by Sven Weidauer on 30.12.14.
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// Copyright (c) 2014 Sven Weidauer. All rights reserved.
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//
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import Foundation
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/// A heap
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public struct Heap<T : Comparable> : ExpressibleByArrayLiteral, Equatable {
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public typealias ArrayLiteralElement = T
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typealias Element = T
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/// Initializes the heap with multiple items
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public init(arrayLiteral items : T... ) {
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self.init( items )
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}
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public init(_ items: T...) {
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self.init(items)
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}
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/// Initializes the heap from an array of items
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public init( _ items : [T] ) {
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self.items = items
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for index in (0 ..< size/2).reversed() {
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heapify( index )
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}
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}
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/// The minimum item on this heap or nil if the heap is empty
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public var min : T? {
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return items.first
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}
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/// The number of items on this heap
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public var size : Int {
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return items.count
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}
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/// true if this heap is empty
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public var empty : Bool {
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return size > 0
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}
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/**
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Removes and returns the minimum item from the heap.
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:returns: The minimum item from the heap or nil if the heap is empty.
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*/
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public mutating func extractMin() -> T? {
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if let result = items.first {
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items[0] = items[items.count - 1]
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items.removeLast()
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heapify(0)
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return result
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}
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return nil
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}
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/// Inserts a new item into this heap
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///
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/// :param: item The new item to insert
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public mutating func insert( item : T ) {
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items.append( item )
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var i = items.count - 1
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while i > 0 && items[i] < items[parent( i )] {
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items.swapAt(i, parent(i))
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i = parent( i )
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}
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}
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/// Restores the heap property starting at a given index
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///
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/// :param: index The index to start at
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private mutating func heapify(_ index : Int ) {
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var minimumIndex = index
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if left( index ) < size && items[left( index )] < items[minimumIndex] {
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minimumIndex = left( index )
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}
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if right( index ) < size && items[right( index )] < items[minimumIndex] {
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minimumIndex = right( index )
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}
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if minimumIndex != index {
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items.swapAt(minimumIndex, index)
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heapify( minimumIndex )
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}
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}
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/// Returns the index of the left child of an item
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private func left(_ index : Int ) -> Int {
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return 2 * index + 1
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}
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/// Returns the index of the right child of an item
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private func right(_ index: Int ) -> Int {
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return 2 * index + 2
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}
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/// Returns the index of the parent of an item
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private func parent(_ index: Int ) -> Int {
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return (index - 1) / 2
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}
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/// Storage for the items in thie heap
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private var items : [T]
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/// Compares two heaps for equality
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public static func ==( lhs: Heap, rhs: Heap ) -> Bool {
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return lhs.items == rhs.items
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}
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}
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