Kotlin函数参数:无法重新分配Val [英] Kotlin function parameter: Val cannot be reassigned

问题描述

我在科特林写了红黑树. Fun insertFixup 在插入新元素( z:Node?是新元素)后恢复平衡.树平衡算法来自此处(第2-3页). 问题是科特林不允许我将 z 重新分配给 z.parent 和 z. parent.parent .我希望 z 成为指针.问题是如何使科特林了解我对他的要求?

I have written Red–black tree in Kotlin. Fun insertFixup restores balance after inserting new element (z: Node? is new element). Algorithm of tree balancing is taken from here (pages 2-3). The problem is that Kotlin does not allow me to reassign z to z.parent and z.parent.parent. I want z to be a pointer. The question is how to make Kotlin understand what I want from him?

class Node(key: Int) {...}

class BinarySearchTree {
    var root: Node? = null

    fun insert(newNode: Node) {...}

    fun RotateLeft(x: Node?) {...}

    fun RotateRight(x: Node?) {...}

    fun insertFixup(z: Node?) {
        var y: Node?
        while (z?.parent?.color == "RED") {
            if (z?.parent == z?.parent?.parent?.left) {
                y = z?.parent?.parent?.right
                if (y?.color == "RED") {
                    z?.parent?.color = "BLACK"
                    y?.color = "BLACK"
                    z?.parent?.parent?.color = "RED"
                    z = z?.parent?.parent
                }
                if (z == z?.parent?.right) {
                    z = z?.parent
                    RotateLeft(z)
                    z?.parent?.color = "BLACK"
                    z?.parent?.parent?.color = "RED"
                    RotateRight(z?.parent?.parent)
                }
            } else {
                y = z?.parent?.parent?.left
                if (y?.color == "RED") {
                    z?.parent?.color = "BLACK"
                    y?.color = "BLACK"
                    z?.parent?.parent?.color = "RED"
                    z = z?.parent?.parent
                }
                if (z != z?.parent?.left) {
                    z = z?.parent
                    RotateLeft(z)
                    z?.parent?.color = "BLACK"
                    z?.parent?.parent?.color = "RED"
                    RotateRight(z?.parent?.parent)
                }
            }
        }
        root?.color = "BLACK"
    }
}

fun main(args: Array<String>) {
    val bst = BinarySearchTree()

    while (true) {
        var newNode = Node(readLine()!!.toInt())
        bst.insert(newNode)
        bst.insertFixup(newNode)
    }
}

UPD :谢谢大家！所有答案都很有帮助，我已经在您的答复中找到了解决方案.

UPD: Thanks to all! All the answers were helpful and I have found the solution in your replies.

推荐答案

Kotlin中的函数参数基本上是函数内部的只读val，因此z此处始终引用传递的原始对象

Function parameters in Kotlin are basically read-only val's inside the function, so z here will always refer to the original object that was passed in.

如果您需要在函数运行时修改指向的内容，则必须在函数开始时对其进行本地复制，然后可以将其设为var.

If you need to modify what it points to while your function is running, you'll have to make a local copy of it at the beginning of the function, and then you can make that a var.

例如，您可以像这样启动您的功能，以便稍后再分配此本地var:

For example, you could start your function like this, which lets you reassign this local var later:

fun insertFixup(_z: Node?) {
    var z = _z
    // ...
    z = z.parent
    // ...
}

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