Why Arrays Exist and What Problem They Solve in DSA Typescript - Test Your Knowledge

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create an array with three numbers.

DSA Typescript

const numbers = [1, 2, [1]];

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

A'3'

B5

Cfour

D3

Attempts:

3 left

💡 Hint

Common Mistakes

Using a string '3' instead of the number 3.

Adding a word like 'four' which is not a number.

The array should contain the number 3 as the third element, not a string or other value.

2fill in blank

medium

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

DSA Typescript

const first = numbers[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 square brackets.

Using curly braces or angle brackets which are incorrect.

Arrays use square brackets with the index number to access elements. Indexing starts at 0.

3fill in blank

hard

Fix the error in the code to add a new element to the array.

DSA Typescript

numbers.[1](4);

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

Aadd

Bappend

Cpush

Dinsert

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'add' or 'append' which are not valid array methods in TypeScript.

Using 'insert' which is not a method on arrays.

The correct method to add an element at the end of an array in TypeScript is push.

4fill in blank

hard

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

DSA Typescript

const squares = [[1]];
for(let i = 1; i <= 5; i++) {
  squares.push(i [2] i);
}

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

A1, 4, 9, 16, 25

B*

C**

D+

Attempts:

3 left

💡 Hint

Common Mistakes

Using '+' instead of '*' which adds numbers instead of multiplying.

Using '**' which is exponentiation but not needed here.

The array starts empty or with the squares listed. The loop multiplies i by i using '*'.

5fill in blank

hard

Fill all three blanks to create a filtered array of even numbers from 1 to 10.

DSA Typescript

const evens = [];
for(let num = 1; num <= 10; num++) {
  if(num [1] 2 === 0) {
    evens.[2](num);
  }
}
console.log(evens); // [3]

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

A%

Bpush

C[2, 4, 6, 8, 10]

Dadd

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'add' instead of 'push' to add elements.

Using '===' incorrectly without modulo operator.

The modulo operator '%' checks for even numbers. The 'push' method adds numbers to the array. The final array contains even numbers from 2 to 10.

Practice

1. Why do arrays exist in programming languages like TypeScript?

easy

A. To store multiple values in a single, ordered collection

B. To perform mathematical calculations automatically

C. To replace all other data structures like trees and graphs

D. To store only one value at a time

Solution

1. Step 1: Understand the purpose of arrays

   Arrays are designed to hold many values together in one place, keeping them in order.

2. Step 2: Compare with other options

   Options A, B, and D do not describe arrays correctly. Arrays do not perform calculations automatically, do not replace all data structures, and can hold more than one value.

3. Final Answer:

   To store multiple values in a single, ordered collection -> Option A

4. Quick Check:

   Arrays store many values in order = C [OK]

Hint: Arrays hold many values together in order [OK]

Common Mistakes:

• Thinking arrays store only one value
• Confusing arrays with calculation tools
• Believing arrays replace all data structures

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

easy

A. let nums: number[] = [1, 2, 3];

B. let nums = (1, 2, 3);

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

D. let nums: array = 1, 2, 3;

Solution

1. Step 1: Check TypeScript array syntax

   In TypeScript, arrays are declared with type followed by square brackets, e.g., number[].

2. Step 2: Validate each option

   let nums: number[] = [1, 2, 3]; uses correct syntax. Options B, C, and D have syntax errors or wrong type declarations.

3. Final Answer:

   let nums: number[] = [1, 2, 3]; -> Option A

4. Quick Check:

   Correct array syntax = A [OK]

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

Common Mistakes:

• Using parentheses instead of brackets
• Assigning array to a single number type
• Incorrect type keyword usage

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

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

medium

A. [10, 20, 30]

B. [10, 20, 30, 40]

C. [40, 10, 20, 30]

D. Error: push is not a function

Solution

1. Step 1: Understand the push method

   The push method adds a new element to the end of the array.

2. Step 2: Apply push to the array

   Starting with [10, 20, 30], pushing 40 results in [10, 20, 30, 40].

3. Final Answer:

   [10, 20, 30, 40] -> Option B

4. Quick Check:

   push adds element at end = D [OK]

Hint: push adds element to array end [OK]

Common Mistakes:

• Thinking push adds element at start
• Expecting original array unchanged
• Confusing push with pop

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

let numbers = 5;
numbers.push(10);

medium

A. Array must be declared with 'const' keyword

B. push method requires two arguments

C. Variable 'numbers' is not an array, so push method is invalid

D. Numbers cannot be stored in arrays

Solution

1. Step 1: Check variable type

   Variable 'numbers' is assigned a single number, not an array.

2. Step 2: Understand push method usage

   push is a method for arrays only, so calling it on a number causes an error.

3. Final Answer:

   Variable 'numbers' is not an array, so push method is invalid -> Option C

4. Quick Check:

   push only works on arrays = A [OK]

Hint: push works only on arrays, not single values [OK]

Common Mistakes:

• Assuming push works on numbers
• Thinking push needs multiple arguments
• Believing arrays must be const

5. You want to store daily temperatures for a week and quickly access any day's temperature by its position. Which data structure solves this problem best and why?

hard

A. Linked list, because it uses less memory than arrays

B. Stack, because it stores data in last-in-first-out order

C. Set, because it automatically removes duplicate temperatures

D. Array, because it stores values in order and allows fast access by index

Solution

1. Step 1: Identify the need for ordered storage and fast access

   Storing temperatures by day means order matters and quick access by position is needed.

2. Step 2: Compare data structures

   Arrays keep order and allow direct access by index, making them ideal. Linked lists have slower access, sets remove duplicates (not needed), stacks use LIFO order which is not suitable.

3. Final Answer:

   Array, because it stores values in order and allows fast access by index -> Option D

4. Quick Check:

   Ordered fast access = Array = B [OK]

Hint: Use arrays for ordered data with fast index access [OK]

Common Mistakes:

• Choosing linked list for fast access
• Using set which removes duplicates unnecessarily
• Selecting stack which reverses order