Swift 二进制搜索树搜索

Question

我正在尝试实现一个存储单词列表的 BST。我知道我的树结构是正确的，因为当我尝试按顺序遍历和打印时，列表按字母顺序打印。但是，我用于在树中查找元素的搜索函数每次都返回 false。

func search(searchValue: String) -> Bool? {
    if searchValue == value as! String{
        return true
    }

    if searchValue < value as! String {
        return left?.search(searchValue: searchValue)
    }
    if searchValue > value as! String{
        return right?.search(searchValue: searchValue)
    }

    return false


}

函数在这个循环中被调用。不在 BST 中的每个单词都应附加到数组 misspelled 中。当前没有单词附加到数组。输入数组是要针对 BST 检查的所有单词的数组。

 for item in arrayInput
        {
            let target = item.lowercased()//reversed
            let inTree = tree.search(searchValue: target)
            if inTree == false
            {
                misspelled.append(item)
            }
        }

上下文的更多 BST 类:

  public class BinarySearchTree<T: Comparable> {
        fileprivate(set) public var value: T
        fileprivate(set) public var parent: BinarySearchTree?
        fileprivate(set) public var left: BinarySearchTree?
        fileprivate(set) public var right: BinarySearchTree?


        public init(value: T) {
            self.value = value
        }

        public convenience init(array: [T]) {
            precondition(array.count > 0)
            self.init(value: array.first!)
            for v in array.dropFirst() {
                insert(value: v)
            }
        }

        }
     public func insert(value: T) {
            if value < self.value {
                if let left = left {
                    left.insert(value: value)
                } else {
                    left = BinarySearchTree(value: value)
                    left?.parent = self
                }
            } else {
                if let right = right {
                    right.insert(value: value)
                } else {
                    right = BinarySearchTree(value: value)
                    right?.parent = self
                }
            }
        }

Answer 1

我对你的代码做了一些改进，看看:

public class BinarySearchTree<T: Comparable> {
    fileprivate(set) public var value: T
    fileprivate(set) public var parent: BinarySearchTree?
    fileprivate(set) public var left: BinarySearchTree?
    fileprivate(set) public var right: BinarySearchTree?


    public init(value: T) {
        self.value = value
    }

    public convenience init(array: [T]) {
        precondition(array.count > 0)
        self.init(value: array.first!)
        for v in array.dropFirst() {
            insert(value: v)
        }
    }

    // Refactored out common code to reduce duplicaiton
    public func insert(value: T) {
        let nodeToModify = value < self.value ? left : right

        if let nodeToModify = nodeToModify {
            nodeToModify.insert(value: value)
        }
        else {
            let subtree = BinarySearchTree(value: value)
            subtree.parent = self
            self.left = subtree
        }
    }


    // Why constrain searching to just Strings? Keep it generic to all T: Comparable
    func search(for searchValue: T) -> Bool {
        if searchValue == value { return true }

        if searchValue < value {
            return left?.search(for: searchValue) ?? false
        }
        if searchValue > value {
            return right?.search(for: searchValue) ?? false
        }

        return false
    }
}

// Move the `search` function outside of the class, and into an extension
// with the constaint that `T == String`
extension BinarySearchTree where T == String {
    func search(for searchValue: String) -> Bool {
        if searchValue == value { return true }

        if searchValue < value {
            return left?.search(for: searchValue) ?? false
        }
        if searchValue > value {
            return right?.search(for: searchValue) ?? false
        }

        return false
    }
}