Heap.swift

/**
 * 堆
 */
public struct Heap<T> {
    
    var nodes = [T]()
    
    private var orderCriteria: (T, T) -> Bool
    
    
    public init(sort: @escaping(T, T) -> Bool) {
        self.orderCriteria = sort
    }
    /// 用数组创建堆
    public init(array: [T], sort: @escaping (T, T) -> Bool) {
        self.orderCriteria = sort
        configureHeap(from: array)
    }
    
    private mutating func configureHeap(from array: [T]) {
        nodes = array
        for i in stride(from: (nodes.count/2 - 1), through: 0, by: -1) {
            shiftDown(i)
        }
    }
    
//    private mutating func buildHeap(fromArray array: [T]) {
//        elements = array
//        for i in stride(from: (nodes.count/2-1), through: 0, by: -1) {
//            shiftDown(index: i, heapSize: elements.count)
//        }
//    }
    
    public var isEmpty: Bool {
        return nodes.isEmpty
    }
    
    public var count: Int {
        return nodes.count
    }
    
    ///
    @inline(__always) internal func parentIndex(ofIndex i: Int) -> Int {
        return (i - 1) / 2
    }
    
    @inline(__always) internal func leftChildIndex(ofIndex i: Int) -> Int {
        return 2*i + 1
    }
    
    @inline(__always) internal func rightChildIndex(ofIndex i: Int) -> Int {
        return 2*i + 2
    }
    
    public func peek() -> T? {
        return nodes.first
    }
    
    public mutating func insert(_ value: T) {
        nodes.append(value)
        shiftUp(nodes.count - 1)
    }
    
    public mutating func insert<S: Sequence>(_ sequence: S) where S.Iterator.Element == T {
        for value in sequence {
            insert(value)
        }
    }
    
    public mutating func replace(index i: Int, value: T) {
        guard i < nodes.count else {
            return
        }
    }
    /// 删除根节点
    @discardableResult public mutating func remove() -> T? {
        guard !nodes.isEmpty else {
            return nil
        }
        
        if nodes.count == 1 {
            return nodes.removeLast()
        } else {
            
            let value = nodes[0]
            nodes[0] = nodes.removeLast()
            shiftDown(0)
            return value
        }
    }
    /// 删除任意节点
    @discardableResult public mutating func remove(at index: Int) -> T? {
        guard index < nodes.count else { return nil }
        
        let size = nodes.count - 1
        if index != size {
            nodes.swapAt(index, size)
            shiftDown(from: index, until: size)
            shiftUp(index)
        }
        return nodes.removeLast()
    }
    /// 向上移动
    internal mutating func shiftUp(_ index: Int) {
        var childIndex = index
        let child = nodes[childIndex]
        var parentIndex = self.parentIndex(ofIndex: childIndex)
        
        while childIndex > 0 && orderCriteria(child, nodes[parentIndex]) {
            nodes[childIndex] = nodes[parentIndex]
            childIndex = parentIndex
            parentIndex = self.parentIndex(ofIndex: childIndex)
        }
        
        nodes[childIndex] = child
    }
    /// 向下移动
    internal mutating func shiftDown(from index: Int, until endIndex: Int) {
        let leftChildIndex = self.leftChildIndex(ofIndex: index)
        let rightChildIndex = leftChildIndex + 1
        
        var first = index
        if leftChildIndex < endIndex && orderCriteria(nodes[leftChildIndex], nodes[first]) {
            first = leftChildIndex
        }
        if rightChildIndex < endIndex && orderCriteria(nodes[rightChildIndex], nodes[first]) {
            first = rightChildIndex
        }
        if first == index { return }
        
        nodes.swapAt(index, first)
        shiftDown(from: first, until: endIndex)
    }
    
    internal mutating func shiftDown(_ index: Int) {
        shiftDown(from: index, until: nodes.count)
    }
}

// MARK: - Searching

extension Heap where T: Equatable {
    
    public func index(of node: T) -> Int? {
        return nodes.index(where: { $0 == node })
    }
    
    @discardableResult public mutating func remove(node: T) -> T? {
        if let index = index(of: node) {
            return remove(at: index)
        }
        return nil
    }
    
}