Inverting a binary tree with javascript

Question

I'm trying to invert a binary tree in javascript, but i can't figure out why I'm not getting it to print my tree. It seems like i can create my tree in the example code in the bottom, but i cant get it to save the data.

// A node contains the value, left and right pointers
class Node {
  constructor(item) {
    this.data = item;
    this.left = this.right = null;
  }
}

class BinaryTree {
  constructor() {
    this.root = null;
  }

  invert() {
    this.root = this.invert(this.root);
  }

  invert(node) {
    if (node == null)
      return node;

    /* recursive calls */
    let left = this.invert(node.left);
    let right = this.invert(node.right);

    /* swap the left and right pointers */
    node.left = right;
    node.right = left;

    return node;
  }

  printTree() {
    this.printTree(this.root);
  }

  // print InOrder binary tree traversal.	
  printTree(node) {
    if (node == null)
      return;

    this.printTree(node.left);
    console.log(node.data + " ");
    this.printTree(node.right);
  }
}

/* testing for example nodes */
const tree = new BinaryTree();
tree.root = new Node(2);
tree.root.left = new Node(11);
tree.root.right = new Node(4);
tree.root.right.left = new Node(13);
tree.root.right.right = new Node(5);

/* log inorder traversal of the input tree */
console.log("Inorder traversal of input tree is :");
tree.printTree();
console.log("");

/* invert tree */
tree.invert();

/* log inorder traversal of the minor tree */
console.log("Inorder traversal of binary tree is : ");
tree.printTree();

What am i doing wrong here to not get it to print the tree, and then invert it.

I have created my own js Binary Tree class. It has function like reverse(), It will reverse all the nodes in tree. npmjs.com/package/@dsinjs/binary-tree Reverse documentation - github.com/dsinjs/binary-tree/blob/main/… — Siddhesh Kulkarni
– Siddhesh Kulkarni, Commented Nov 29, 2020 at 19:23

dave · Accepted Answer · 2020-02-17 22:46:48Z

1

You can't overload functions in javascript, it will always call the same function regardless of which one "matches".

class Demo {
    overload(a) {
        console.log('hi');
    }
    overload() {
        console.log('bye');
    }
    overload(a, b) {
        console.log('wow');
    }
}

const d = new Demo();
d.overload();
d.overload(1);
d.overload(1, 2);

Because you start with tree.printTree();, and it's actually calling:

printTree(node) {
  if (node == null)
    return;

  this.printTree(node.left);
  console.log(node.data + " ");
  this.printTree(node.right);
}

AND you used == instead of ===, you are essentially calling:

printTree() {
    if (true) {
        return;
    }
}

answered Feb 17, 2020 at 22:46

dave

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