如何从递归 getHeight 方法修复堆栈溢出

Question

当我为计算二叉搜索树高度的方法运行代码时，会导致堆栈溢出错误，但仅适用于具有多个节点的树（我的程序中的 BSTElements）。我读到这是由于错误的递归调用，但无法在我的代码中识别问题。

public int getHeight() {

    return getHeight(this.getRoot());
}

private int getHeight(BSTElement<String,MorseCharacter> element) {

    int height=0;

    if (element == null) {
        return -1;
    }

    int leftHeight = getHeight(element.getLeft());
    int rightHeight = getHeight(element.getRight());

    if (leftHeight > rightHeight) {
        height = leftHeight;
    } else {
        height = rightHeight;
    }

    return height +1;
}

这里是完整的代码：

public class MorseCodeTree {

private static BSTElement<String, MorseCharacter> rootElement;



public BSTElement<String, MorseCharacter> getRoot() {
    return rootElement;
}

public static void setRoot(BSTElement<String, MorseCharacter> newRoot) {
    rootElement = newRoot;
}



public MorseCodeTree(BSTElement<String,MorseCharacter> element) {
    rootElement = element;
}

public MorseCodeTree() {
    rootElement = new BSTElement("Root",  "", new MorseCharacter('\0', null));
}
    public int getHeight() {

    return getHeight(this.getRoot());
}

private int getHeight(BSTElement<String,MorseCharacter> element) {

    if (element == null) {
        return -1;
    } else {
        int leftHeight = getHeight(element.getLeft());
        int rightHeight = getHeight(element.getRight());


    if (leftHeight < rightHeight) {
        return rightHeight + 1;
    } else {
        return leftHeight + 1;
    }
    }
}
public static boolean isEmpty() {
        return (rootElement == null);   
}

public void clear() {
    rootElement = null;
}

public static void add(BSTElement<String,MorseCharacter> newElement) {

        BSTElement<String, MorseCharacter> target = rootElement;
        String path = "";
        String code = newElement.getKey();

        for (int i=0; i<code.length(); i++) {
            if (code.charAt(i)== '.') {
                if (target.getLeft()!=null) {
                    target=target.getLeft();
                } else {
                    target.setLeft(newElement);
                    target=target.getLeft();
                }

            } else {
                if (target.getRight()!=null) {
                    target=target.getRight();
                } else {
                    target.setRight(newElement);
                    target=target.getRight();
                }   
            }
        }
        MorseCharacter newMorseChar = newElement.getValue();

        newElement.setLabel(Character.toString(newMorseChar.getLetter()));
        newElement.setKey(Character.toString(newMorseChar.getLetter()));
        newElement.setValue(newMorseChar);

}

    public static void main(String[] args) {
    MorseCodeTree tree = new MorseCodeTree();
        BufferedReader reader;

    try {
        reader = new BufferedReader(new FileReader(file));
        String line = reader.readLine();


        while (line != null) {

            String[] output = line.split(" ");
            String letter = output[0];
            MorseCharacter morseCharacter = new MorseCharacter(letter.charAt(0), output[1]);

            BSTElement<String, MorseCharacter> bstElement = new BSTElement(letter, output[1], morseCharacter);

            tree.add(bstElement);

            line = reader.readLine();

            System.out.println(tree.getHeight());
        }
        reader.close();




    } catch (IOException e) {
    System.out.println("Exception" + e);
    }

Answer 1

您向我们展示的代码似乎没有任何明显错误¹。

如果此代码为一棵小树提供StackOverflowException，那很可能意味着您的树创建不正确并且其中有一个循环（循环）。如果您的递归算法在“树”中遇到循环，它将循环直到堆栈溢出²。

为了确定这一诊断，我们需要查看一个 MVCE，其中包含构建展示该行为的示例树所需的所有代码。

---

^{1 - 高度计算中可能存在“off by one”错误，但这不会导致堆栈溢出。}

^{2 - 当前的 Java 实现不进行尾调用优化。}