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.

Practice

1. What is the main purpose of serialize and deserialize functions in the context of a binary tree?

easy

A. Sort the nodes of a binary tree in ascending order

B. Convert a binary tree to a string and back to a binary tree

C. Calculate the height of a binary tree

D. Delete all nodes in a binary tree

Solution

1. Step 1: Understand serialization

   Serialization means converting a data structure like a binary tree into a string format that can be stored or transmitted.

2. Step 2: Understand deserialization

   Deserialization means converting the string back into the original binary tree structure.

3. Final Answer:

   Convert a binary tree to a string and back to a binary tree -> Option B

4. Quick Check:

   Serialize/deserialize = convert tree to/from string [OK]

Hint: Think of saving and loading a tree as text [OK]

Common Mistakes:

• Confusing serialization with sorting
• Thinking it deletes nodes
• Mixing with tree height calculation

2. Which of the following is the correct way to declare a function in JavaScript for serializing a binary tree?

easy

A. function: serialize(root) { /* code */ }

B. serialize function(root) { /* code */ }

C. def serialize(root): { /* code */ }

D. function serialize(root) { /* code */ }

Solution

1. Step 1: Recall JavaScript function syntax

   In JavaScript, functions are declared using the keyword function followed by the name and parameters.

2. Step 2: Check each option

   function serialize(root) { /* code */ } uses correct syntax. Options A, B, and D use invalid or other language syntax.

3. Final Answer:

   function serialize(root) { /* code */ } -> Option D

4. Quick Check:

   JS function declaration = function name(params) [OK]

Hint: Use 'function name(params)' to declare in JS [OK]

Common Mistakes:

• Using Python or other language syntax
• Missing the 'function' keyword
• Using colons or wrong punctuation

3. What will be the output of the following code snippet?

class TreeNode {
  constructor(val, left = null, right = null) {
    this.val = val;
    this.left = left;
    this.right = right;
  }
}

function serialize(root) {
  if (!root) return '#';
  return root.val + ',' + serialize(root.left) + ',' + serialize(root.right);
}

const root = new TreeNode(1, new TreeNode(2), new TreeNode(3));
console.log(serialize(root));

medium

A. "1,2,#,#,3,#,#"

B. "1,2,3,#,#,#,#"

C. "1,#,2,#,3,#,#"

D. "#,#,1,2,3"

Solution

1. Step 1: Understand the serialize function

   The function uses preorder traversal: root, left, right. Null nodes are represented by '#'.

2. Step 2: Trace the tree serialization

   Root is 1, left child 2 (with no children), right child 3 (with no children). So serialization is "1,2,#,#,3,#,#".

3. Final Answer:

   "1,2,#,#,3,#,#" -> Option A

4. Quick Check:

   Preorder with '#' for null = "1,2,#,#,3,#,#" [OK]

Hint: Preorder traversal with '#' for null nodes [OK]

Common Mistakes:

• Confusing preorder with inorder or postorder
• Forgetting to add '#' for null children
• Mixing order of nodes in output

4. Identify the error in the following deserialize function for a binary tree:

function deserialize(data) {
  const values = data.split(',');
  function build() {
    if (values.length === 0) return null;
    const val = values.shift();
    if (val === '#') return null;
    const node = new TreeNode(val);
    node.left = build();
    node.right = build();
    return node;
  }
  return build();
}

medium

A. The TreeNode constructor should convert val to number

B. The function does not handle empty input string

C. The values array should be reversed before processing

D. The function should use pop() instead of shift()

Solution

1. Step 1: Analyze the deserialize function

   The function splits the string and uses shift() to get values in order, which is correct.

2. Step 2: Check TreeNode value type

   Values from split are strings. If TreeNode expects numbers, val should be converted using Number(val) or +val.

3. Final Answer:

   The TreeNode constructor should convert val to number -> Option A

4. Quick Check:

   Convert string to number for node values [OK]

Hint: Convert string values to numbers when creating nodes [OK]

Common Mistakes:

• Ignoring type conversion of node values
• Reversing array unnecessarily
• Using pop() breaks preorder order

5. Given the serialized string "1,2,#,#,3,4,#,#,5,#,#", which of the following binary trees is the correct deserialized structure?

hard

A. Root 1 with left child 3, right child 2 with children 4 and 5

B. Root 1 with left child 2 with children 4 and 5, right child 3 (no children)

C. Root 1 with left child 2 (no children), right child 3 with left 4 and right 5

D. Root 1 with left child 4, right child 5 with children 2 and 3

Solution

1. Step 1: Understand the serialized string format

   The string uses preorder traversal with '#' for nulls: root, left subtree, right subtree.

2. Step 2: Trace the tree structure

   Root is 1, left child 2 with no children (#,#), right child 3 with left child 4 (no children) and right child 5 (no children).

3. Final Answer:

   Root 1 with left child 2 (no children), right child 3 with left 4 and right 5 -> Option C

4. Quick Check:

   Preorder string matches tree structure in Root 1 with left child 2 (no children), right child 3 with left 4 and right 5 [OK]

Hint: Draw preorder steps to visualize tree structure [OK]

Common Mistakes:

• Mixing left and right children
• Ignoring '#' as null nodes
• Misreading preorder order