Serialize and Deserialize Binary Tree in DSA Typescript - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a new node with the given value.

DSA Typescript

class TreeNode {
  val: number;
  left: TreeNode | null;
  right: TreeNode | null;
  constructor(val: number) {
    this.val = [1];
    this.left = null;
    this.right = null;
  }
}

Drag options to blanks, or click blank then click option'

Avalue

Bval

Cnode

Ddata

Attempts:

3 left

💡 Hint

Common Mistakes

Using a variable name not defined in the constructor.

Assigning 'this.val' to a wrong variable.

The constructor parameter is named 'val', so we assign 'this.val = val;' to set the node's value.

2fill in blank

medium

Complete the code to serialize the binary tree using preorder traversal.

DSA Typescript

function serialize(root: TreeNode | null): string {
  const result: string[] = [];
  function dfs(node: TreeNode | null) {
    if (node === null) {
      result.push('null');
      return;
    }
    result.push(node.val.toString());
    dfs(node.[1]);
    dfs(node.right);
  }
  dfs(root);
  return result.join(',');
}

Drag options to blanks, or click blank then click option'

Aval

Broot

Cright

Dleft

Attempts:

3 left

💡 Hint

Common Mistakes

Calling dfs on the right child before the left child.

Using an incorrect property name.

In preorder traversal, we visit the left child before the right child, so we call dfs(node.left) first.

3fill in blank

hard

Fix the error in the deserialize function to correctly parse the next node value.

DSA Typescript

function deserialize(data: string): TreeNode | null {
  const values = data.split(',');
  let index = 0;
  function dfs(): TreeNode | null {
    if (values[[1]] === 'null') {
      index++;
      return null;
    }
    const node = new TreeNode(parseInt(values[index]));
    index++;
    node.left = dfs();
    node.right = dfs();
    return node;
  }
  return dfs();
}

Drag options to blanks, or click blank then click option'

A1

B0

Cindex

Dvalues.length

Attempts:

3 left

💡 Hint

Common Mistakes

Checking a fixed index like 0 or 1 instead of the current index.

Using values.length which is out of bounds.

We must check the current index position in the values array to see if it is 'null'.

4fill in blank

hard

Fill in the blank to correctly implement the base case in deserialize.

DSA Typescript

function deserialize(data: string): TreeNode | null {
  const values = data.split(',');
  let index = 0;
  function dfs(): TreeNode | null {
    if (values[index] [1] 'null') {
      index++;
      return null;
    }
    const node = new TreeNode(parseInt(values[index]));
    index++;
    node.left = dfs();
    node.right = dfs();
    return node;
  }
  return dfs();
}

Drag options to blanks, or click blank then click option'

A===

B!==

C<

D>

Attempts:

3 left

💡 Hint

Common Mistakes

Using '!=' or '!==', which would invert the condition.

Using comparison operators like '<' or '>'.

The base case checks if the current value is exactly 'null' using '===' operator.

5fill in blank

hard

Fill all three blanks to complete the serialize function using preorder traversal with null markers.

DSA Typescript

function serialize(root: TreeNode | null): string {
  const result: string[] = [];
  function dfs(node: TreeNode | null) {
    if (node === [1]) {
      result.push([2]);
      return;
    }
    result.push(node.val.toString());
    dfs(node.left);
    dfs(node.[3]);
  }
  dfs(root);
  return result.join(',');
}

Drag options to blanks, or click blank then click option'

Anull

B'null'

Cright

Dundefined

Attempts:

3 left

💡 Hint

Common Mistakes

Checking for undefined instead of null.

Pushing null instead of the string 'null'.

Recursing on the wrong child.

We check if node is null, push the string 'null', and recurse on the right child.