Serialize and Deserialize Binary Tree in DSA Javascript - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

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

DSA Javascript

function TreeNode(val) {
  this.val = [1];
  this.left = null;
  this.right = null;
}

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

Aval

Bvalue

Cdata

Dnode

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different variable name than the parameter.

Assigning undefined or null instead of the parameter.

The constructor should assign the passed value to this.val. The parameter name is val.

2fill in blank

medium

Complete the code to add a node's value to the result array during serialization.

DSA Javascript

function serialize(root) {
  const result = [];
  function dfs(node) {
    if (!node) {
      result.push('null');
      return;
    }
    result.push(node[1]);
    dfs(node.left);
    dfs(node.right);
  }
  dfs(root);
  return result.join(',');
}

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

A.node

B.value

C.val

D.data

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect property names like 'value' or 'data'.

Trying to push the whole node instead of its value.

The node's value is stored in the val property, so we use node.val.

3fill in blank

hard

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

DSA Javascript

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

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

A.shift()

B[1]

C[0]

D.pop()

Attempts:

3 left

💡 Hint

Common Mistakes

Using indexing without removing the element causes infinite loops.

Using pop removes the last element, which is incorrect here.

We must remove the first value from the array before using it, so values.shift() returns and removes the first element.

4fill in blank

hard

Fill both blanks to correctly serialize a binary tree using preorder traversal.

DSA Javascript

function serialize(root) {
  const result = [];
  function dfs(node) {
    if (node === null) {
      result.push([1]);
      return;
    }
    result.push(node[2]);
    dfs(node.left);
    dfs(node.right);
  }
  dfs(root);
  return result.join(',');
}

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

A'null'

Bnull

C.val

D.value

Attempts:

3 left

💡 Hint

Common Mistakes

Using null (without quotes) instead of 'null' string.

Using incorrect property names like 'value'.

We push the string 'null' for empty nodes and the node's value using node.val.

5fill in blank

hard

Fill all three blanks to correctly deserialize a binary tree from a string.

DSA Javascript

function deserialize(data) {
  const values = data.split(',');
  function dfs() {
    if (values[1] === [2]) {
      values.shift();
      return [3];
    }
    const node = new TreeNode(parseInt(values.shift()));
    node.left = dfs();
    node.right = dfs();
    return node;
  }
  return dfs();
}

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

A[0]

B'null'

Cnull

D[1]

Attempts:

3 left

💡 Hint

Common Mistakes

Comparing to null instead of 'null' string.

Using wrong index or removing elements incorrectly.

We check if the first element is the string 'null' (values[0] === 'null'), then remove it and return null for empty nodes.