Arrays vs Other Data Structures When to Choose Arrays in DSA Typescript - Interactive Comparison Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create an array of numbers.

DSA Typescript

const numbers: number[] = [1, 2, 3, [1]];

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

A'4'

Bfive

C4

Dnull

Attempts:

3 left

💡 Hint

Common Mistakes

Using a string '4' instead of number 4.

Using a non-number like 'five' or null.

The array should contain numbers only. Using 4 (number) is correct.

2fill in blank

medium

Complete the code to access the first element of the array.

DSA Typescript

const first = fruits[1];

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

A(0)

B[0]

C{0}

D.0

Attempts:

3 left

💡 Hint

Common Mistakes

Using parentheses () instead of brackets.

Using dot notation with numbers.

Arrays use square brackets to access elements by index.

3fill in blank

hard

Fix the error in the code to add an element to the end of the array.

DSA Typescript

numbers.[1](5);

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

Aadd

Bappend

Cinsert

Dpush

Attempts:

3 left

💡 Hint

Common Mistakes

Using non-existent methods like add or append.

Confusing push with insert.

The push method adds an element to the end of an array in TypeScript.

4fill in blank

hard

Fill both blanks to create an array of squares for numbers 1 to 5.

DSA Typescript

const squares = [[1]].map(x => x [2] x);

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

A1, 2, 3, 4, 5

Bx * x

Cx + x

D5, 4, 3, 2, 1

Attempts:

3 left

💡 Hint

Common Mistakes

Using addition instead of multiplication.

Reversing the array order.

The array should list numbers 1 to 5, and the map function squares each number using x * x.

5fill in blank

hard

Fill all three blanks to filter even numbers and create a new array.

DSA Typescript

const evens = numbers.filter(n => n [1] 2 === 0).[2](n => n [3] 1);

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

A%

Bmap

C+

D-

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong operators for modulo or addition.

Using filter instead of map for transformation.

Use % to check even numbers, map to transform, and + to add 1.

Practice

1. Which of the following is the best reason to choose an array over other data structures like linked lists or trees?

easy

A. You need to store key-value pairs.

B. You need fast access to elements by index.

C. You want to insert elements frequently in the middle.

D. You want to maintain a sorted order automatically.

Solution

1. Step 1: Understand array access speed

   Arrays allow direct access to elements using their index in constant time (O(1)).

2. Step 2: Compare with other structures

   Linked lists or trees do not provide constant time index access; they require traversal.

3. Final Answer:

   You need fast access to elements by index. -> Option B

4. Quick Check:

   Fast index access = Array [OK]

Hint: Arrays excel at fast index access, unlike linked lists [OK]

Common Mistakes:

• Choosing arrays for frequent middle insertions
• Confusing arrays with key-value stores
• Assuming arrays keep data sorted automatically

2. Which of the following is the correct way to declare an array of numbers in TypeScript?

easy

A. let arr = {1, 2, 3};

B. let arr: array = (1, 2, 3);

C. let arr: number[] = [1, 2, 3];

D. let arr: number = [1, 2, 3];

Solution

1. Step 1: Recall TypeScript array syntax

   Arrays of numbers are declared as number[] with square brackets after the type.

2. Step 2: Check each option

   let arr: number[] = [1, 2, 3]; uses correct syntax: let arr: number[] = [1, 2, 3];. Others have syntax errors or wrong types.

3. Final Answer:

   let arr: number[] = [1, 2, 3]; -> Option C

4. Quick Check:

   TypeScript array syntax = let arr: number[] = [1, 2, 3]; [OK]

Hint: Use type[] to declare arrays in TypeScript [OK]

Common Mistakes:

• Using parentheses instead of square brackets
• Assigning array to a non-array type
• Using curly braces which define objects

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

const arr = [10, 20, 30, 40];
console.log(arr[2]);
arr[2] = 50;
console.log(arr);

medium

A. 30 and then [10, 20, 50, 40]

B. [10, 20, 30, 40] and then [10, 20, 50, 40]

C. 30 and then [10, 20, 30, 40]

D. Error because arrays are immutable

Solution

1. Step 1: Check first console.log output

   Accessing arr[2] returns the third element, which is 30.

2. Step 2: Update array and check second console.log

   Setting arr[2] = 50 changes the third element. Printing arr shows [10, 20, 50, 40].

3. Final Answer:

   30 and then [10, 20, 50, 40] -> Option A

4. Quick Check:

   Index access then update = 30 and then [10, 20, 50, 40] [OK]

Hint: Arrays allow element update by index directly [OK]

Common Mistakes:

• Thinking arrays are immutable in TypeScript
• Confusing index 2 with index 3
• Expecting original array after update

4. Identify the error in the following TypeScript code that tries to add an element to an array:

const numbers = [1, 2, 3];
numbers.add(4);

medium

A. The array must be initialized with 'new Array()' to add elements.

B. The array should be declared with 'let' to add elements.

C. The number 4 must be inside square brackets.

D. Arrays don't have an 'add' method; use 'push' instead.

Solution

1. Step 1: Check method used on array

   The method add does not exist for arrays in TypeScript or JavaScript.

2. Step 2: Identify correct method to add elements

   To add elements, use push method like numbers.push(4).

3. Final Answer:

   Arrays don't have an 'add' method; use 'push' instead. -> Option D

4. Quick Check:

   Use push, not add, to add array elements [OK]

Hint: Use push() to add elements to arrays [OK]

Common Mistakes:

• Using non-existent 'add' method
• Thinking 'let' is required to modify array contents
• Trying to add elements with wrong syntax

5. You need to store a large collection of items where you frequently access elements by index and rarely insert or delete items. Which data structure should you choose and why?

hard

A. Array, because it provides fast index-based access and low memory overhead.

B. Linked List, because it allows fast insertions and deletions.

C. Hash Map, because it stores key-value pairs efficiently.

D. Binary Tree, because it keeps data sorted automatically.

Solution

1. Step 1: Analyze access and modification needs

   Frequent index-based access means we want constant time access by position.

2. Step 2: Compare data structures for this use case

   Arrays provide O(1) access by index and use less memory. Insertions/deletions are rare, so array's slower modification is acceptable.

3. Final Answer:

   Array, because it provides fast index-based access and low memory overhead. -> Option A

4. Quick Check:

   Fast index access + rare changes = Array [OK]

Hint: Choose arrays for fast index access and few modifications [OK]

Common Mistakes:

• Choosing linked list despite rare insertions
• Confusing hash maps with index-based access
• Assuming binary trees are best for all data