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public enum BinaryTreeChildSide { | |
case left, right | |
} | |
public struct BinaryTreeIterator<Tree: BinaryTree>: Sequence, IteratorProtocol { | |
private let tree: Tree | |
private var stack: [Tree.Index] | |
private var index: Tree.Index? | |
private init(_ tree: Tree) { | |
self.tree = tree | |
stack = [] | |
index = tree.rootIndex | |
} | |
public mutating func next() -> Tree.Element? { | |
while let theIndex = index { | |
stack.append(theIndex) | |
index = tree.child(of: theIndex, side: .left) | |
} | |
guard let currentIndex = stack.popLast() else { return nil } | |
defer { index = tree.child(of: currentIndex, side: .right) } | |
return tree[currentIndex] | |
} | |
} | |
public protocol BinaryTree { | |
associatedtype Element | |
associatedtype Index | |
func child(of index: Index, side: BinaryTreeChildSide) -> Index? | |
var rootIndex: Index? { get } | |
subscript(position: Index) -> Element { get } | |
} | |
public struct BinaryHeap<Element> { | |
private var elements: [Element] | |
public init(_ elements: [Element]) { | |
self.elements = elements | |
} | |
} | |
public extension BinaryTree { | |
func makeIterator() -> BinaryTreeIterator<Self> { | |
return BinaryTreeIterator(self) | |
} | |
} | |
extension BinaryHeap: BinaryTree { | |
private func safeIndexOrNil(_ index: Int) -> Int? { | |
return elements.indices.contains(index) ? index : nil | |
} | |
public func child(of index: Int, side: BinaryTreeChildSide) -> Int? { | |
switch side { | |
case .left: return safeIndexOrNil(index * 2 + 1) | |
case .right: return safeIndexOrNil(index * 2 + 2) | |
} | |
} | |
public var rootIndex: Int? { return safeIndexOrNil(0) } | |
public subscript(position: Int) -> Element { | |
return elements[position] | |
} | |
} | |
let heap = BinaryHeap([4, 2, 6, 1, 3, 5, 7]) | |
var iterator = heap.makeIterator() | |
while let next = iterator.next() { | |
print(next, terminator: " ") | |
} | |
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