Trying to get BST`s depth but I can't in JS

Question

I am trying to get Binary Search Tree`s depth using Node and BinarySearch Tree classes down here

class Node{

    constructor(data) {
        this.data = data;
        this.left = null;
        this.right = null;
    }
}

class BinarySearchTree {
    constructor() {

        this.root = null;

    }

    insert(data) {

        //creating a new node and initialising with data.
        const newNode = new Node(data);

        if (this.root === null)
            this.root = newNode;
        else
            this.insertNode(this.root, newNode);

    }

    // Method to insert a node in a tree
    // it moves over the tree to find the location
    // to insert a node with a given data
    insertNode(node, newNode) {

        //if the data is less then the node move left
        if (newNode.data < node.data) {
            if (node.left === null)
                node.left = newNode;
            else
                //Recursively calling function in order to go deeper
                this.insertNode(node.left, newNode);

        }
        //if the data is more than the node move right
        else {
            if (node.right === null)
                node.right = newNode;
            else
                //if right node not null recursively call the function again in order to go deeper the tree.
                this.insertNode(node.right, newNode);
        }
    }
}

And Run getDepth function in here. I tried to add safeguards to check if tree.right is null or not still I get depthright and depthleft variables as nulls.

 function getDepth(tree){

    let depthleft  = 0, depthright = 0;
    
    if (tree === null){
        console.log("TREE "+JSON.stringify(tree));
        return 0;
    }else if (tree["left"] === null && tree["right"] === null ){
        return 1;

    }else {

            depthleft = 1 +  getDepth(tree["left"]);
            depthright = 1 +  getDepth(tree["right"]);

        if (depthright > depthleft){

            console.log("DR "+ depthright);
        }else{
            console.log("treeleft "+ JSON.stringify(tree["left"]));

            console.log("DllllllllL5 "+ JSON.stringify(depthleft));
            console.log("DlRRRRRRL5 "+ JSON.stringify(depthright));

        }
    }
}

function run(arr){

    const tree = new BinarySearchTree();

    for (const elem of arr){
        tree.insert(elem);
    }

    getDepth(tree.root);

}
run([12,7,19,5,9,10]);

But when I console log depthleft and depthright in getDepth function they become null at some point and it does not work?

Where I am doing wrong?

Answer 1

In the getDepth() function, you're not returning anything if the node isn't a leaf node. That causes the depth to become null during the traversal. You can fix it by simply returning the correct depth.

function getDepth(tree){
    let depthleft  = 0, depthright = 0;
    if (tree === null) { return 0; }
    else if (tree["left"] === null && tree["right"] === null ) { return 1; }
    else {
        depthleft = 1 +  getDepth(tree["left"]);
        depthright = 1 +  getDepth(tree["right"]);
        return Math.max(depthleft, depthright);
    }
}

Running this for your input correctly return 4.