Question

打印AVL树数据的可能方法是什么？有可能用ANTLR来实现每个节点中的数据可视化，这样我也可以验证平衡吗？

谢谢！

Answer 1

我在Java完成了这项工作，而不是JavaScript。但是，您只需要翻译语法。算法是一样的。假设你使用了指针，你的Node类看起来如下：

// However this would be implemented in JavaScript
public class BinarySearchTreeNode<K, V> {
    BinarySearchTreeNode left;
    BinarySearchTreeNode right;
    K key;
    V value;
}

这是我打印树的方式：

// This function starts it off at the root
// and calls the real function
public String toTreeString() {
    return this.toTreeString("", true, "", root);
}

// Keep concatenating the string
private String toTreeString(String prefix, boolean top, String tree, BinarySearchTreeNode<K, V> node) {
    BinarySearchTreeNode<K, V> left;
    BinarySearchTreeNode<K, V> right;
    String temp;

    // If we were passed an empty tree
    if (node == null) {
        return "";
    }

    // Get children nodes
    left = node.leftChild;
    right = node.rightChild;

    // If the right child is not null
    if (right != null) {

        // Draw a path to the node
        temp = path(top, "" + prefix, "│   ", "    ");

        // Recursively append to right subtree
        tree = toTreeString(temp, false, tree, right);
    }

    // Draw a path to this node
    tree = path(top, tree + prefix, "└──", "┌──");

    // Append this node to the tree
    tree += " " + node.key + "\n";

    // If the left child is not null
    if (left != null) {

        // Draw a path to the node
        temp = path(top, "" + prefix, "    ", "│   ");

        // Recursively append left sub tree
        tree = toTreeString(temp, true, tree, left);
    }

    return tree;
}

//------------------------------------------------------------------------------

private String path(boolean condition, String s, String choice1, String choice2) {

    if (condition) {
        s += choice1;
    } else {
        s += choice2;
    }

    return s;
}

一旦你有一个树构建，你就会传递

// Your implementation of AVL Tree
import structures.trees.AVLTree;

public final class Application {

  public static void main(String[] args) {

    AVLTree<Integer, Integer> tree = new AVLTree<>();

    tree.insert(1, null);
    tree.insert(4, null);
    tree.insert(3, null);
    tree.insert(0, null);
    tree.insert(6, null);
    tree.insert(9, null);
    tree.insert(8, null);
    tree.insert(3, null);

    String treeString = tree.toTreeString();

    System.out.println(treeString);
    System.out.println("IsBalanced: " + tree.isBalanced());
  }

}

输出：

│       ┌── 9
│       │   └── 8
│   ┌── 6
│   │   └── 4
└── 3
    └── 1
        └── 0

IsBalanced: true

如果您使用数组实现AVL树，则实现几乎为identical

然而：这只适用于小树。对于大树来说，阅读起来并不容易。您应该使用算法来检查树是否以编程方式平衡：

private int isBalanced(BinarySearchTreeNode<K, V> node) {
    if (node == null)
        return 0;

    // Get heights of subtrees
    int h1 = isBalanced(node.leftChild);
    int h2 = isBalanced(node.rightChild);

    if (h1 == -1 || h2 == -1)
        return -1;

    if (Math.abs(h1 - h2) > 1)
        return -1;

    if (h1 > h2)
        return h1 + 1;
    else
        return h2 + 1;
}

以可读格式打印ALV树

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