Array Insertion at End in DSA Typescript - Practice Problems & Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output after inserting elements at the end of the array?

Consider the following TypeScript code that inserts elements at the end of an array. What will be the final state of the array printed?

DSA Typescript

let arr: number[] = [1, 2, 3];
arr.push(4);
arr.push(5);
console.log(arr);

A [4, 5, 1, 2, 3]

B [1, 2, 3, 4, 5]

C [1, 2, 3]

D [5, 4, 3, 2, 1]

💡 Hint

Remember that push adds elements to the end of the array.

The push method adds elements to the end of the array, so after pushing 4 and 5, the array becomes [1, 2, 3, 4, 5].

❓ Predict Output

intermediate

What is the output after multiple insertions at the end?

What will be printed after running this TypeScript code?

DSA Typescript

const numbers: number[] = [];
numbers.push(10);
numbers.push(20);
numbers.push(30);
console.log(numbers);

A [30, 20, 10]

B [10, 20]

C []

D [10, 20, 30]

💡 Hint

Each push adds one element at the end.

Starting from an empty array, pushing 10, 20, and 30 adds them in order at the end, resulting in [10, 20, 30].

🔧 Debug

advanced

Identify the error in this array insertion code

What error will this TypeScript code produce when trying to insert elements at the end of the array?

DSA Typescript

let arr: number[] = [1, 2, 3];
arr.push(4, 5);
arr.push('6');
console.log(arr);

A TypeError: Argument of type 'string' is not assignable to parameter of type 'number'.

B TypeError: arr.push is not a function

C No error, output: [1, 2, 3, 4, 5, '6']

D SyntaxError: Unexpected string

💡 Hint

Check the type of elements pushed to the array.

The array is typed to hold numbers only. Pushing a string '6' causes a type error in TypeScript.

❓ Predict Output

advanced

What is the output after inserting elements using length property?

What will be the output of this TypeScript code that inserts elements at the end using the length property?

DSA Typescript

let arr: number[] = [5, 6];
arr[arr.length] = 7;
arr[arr.length] = 8;
console.log(arr);

A [5, 6, 7, 8]

B [7, 8, 5, 6]

C [5, 6]

D [5, 6, undefined, 7, 8]

💡 Hint

Using arr.length as index adds elements at the end.

Assigning to arr[arr.length] adds elements at the end of the array, so the final array is [5, 6, 7, 8].

🧠 Conceptual

expert

Why is push preferred over direct length assignment for insertion?

Which of the following is the best reason to prefer using push() over assigning to arr[arr.length] when inserting at the end of an array in TypeScript?

A push() can only add one element at a time, making it safer.

B Assigning to arr[arr.length] is faster and more readable.

C push() automatically updates the array length and is less error-prone.

D Assigning to arr[arr.length] throws an error if the array is empty.

💡 Hint

Think about safety and automatic updates.

push() method safely adds elements at the end and updates length automatically, reducing errors compared to manual index assignment.

Practice

1. What does inserting an element at the end of an array do?

easy

A. Adds the element as the last item in the array

B. Removes the first element of the array

C. Replaces the first element with the new element

D. Sorts the array in ascending order

Solution

1. Step 1: Understand array insertion

   Inserting at the end means adding a new element after the last existing element.

2. Step 2: Effect on array

   The new element becomes the last item, increasing the array size by one.

3. Final Answer:

   Adds the element as the last item in the array -> Option A

4. Quick Check:

   Insertion at end = append last [OK]

Hint: Insertion at end means append after last element [OK]

Common Mistakes:

• Confusing insertion at end with removal
• Thinking insertion replaces elements
• Assuming insertion sorts the array

2. Which of the following is the correct TypeScript syntax to insert an element `5` at the end of array `arr`?

easy

A. arr.insert(5);

B. arr.add(5);

C. arr.push(5);

D. arr.append(5);

Solution

1. Step 1: Identify correct method for insertion at end

   In TypeScript (JavaScript), the method to add at the end is `push()`.

2. Step 2: Check other options

   Methods `add()`, `insert()`, and `append()` do not exist on arrays in TypeScript.

3. Final Answer:

   arr.push(5); -> Option C

4. Quick Check:

   Use push() to add at end [OK]

Hint: Use push() method to add at array end [OK]

Common Mistakes:

• Using non-existent methods like add or append
• Confusing push() with pop()
• Trying to assign directly to arr[arr.length]

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

let arr = [1, 2, 3];
arr.push(4);
console.log(arr);

medium

A. [4, 1, 2, 3]

B. [1, 2, 3, 4]

C. [1, 2, 3]

D. [1, 2, 4, 3]

Solution

1. Step 1: Initial array state

   Array starts as [1, 2, 3].

2. Step 2: Apply push(4)

   push(4) adds 4 at the end, so array becomes [1, 2, 3, 4].

3. Final Answer:

   [1, 2, 3, 4] -> Option B

4. Quick Check:

   push adds element at end [OK]

Hint: push() adds element at array end [OK]

Common Mistakes:

• Thinking push adds at start
• Confusing push with unshift
• Expecting array to remain unchanged

4. Identify the error in the following TypeScript code that tries to insert `10` at the end of array `nums`.

let nums = [1, 2, 3];
nums.push = 10;
console.log(nums);

medium

A. Using assignment instead of calling push method

B. Array nums is not declared properly

C. push method does not exist on arrays

D. Console.log syntax is incorrect

Solution

1. Step 1: Analyze push usage

   The code assigns 10 to nums.push instead of calling nums.push(10).

2. Step 2: Effect of assignment

   This overwrites the push method, so no insertion happens and push is lost.

3. Final Answer:

   Using assignment instead of calling push method -> Option A

4. Quick Check:

   push must be called as a function [OK]

Hint: Call push() as a function, don't assign to it [OK]

Common Mistakes:

• Assigning value to push instead of calling it
• Forgetting parentheses after push
• Assuming push is a property, not a method

5. Given an empty array `let data: number[] = [];`, which code snippet correctly inserts numbers 1 to 3 at the end of the array using a loop?

hard

A. for(let i = 0; i < 3; i++) { data.push(i); }

B. for(let i = 1; i <= 3; i++) { data[i] = i; }

C. for(let i = 1; i < 3; i++) { data.push(i); }

D. for(let i = 1; i <= 3; i++) { data.push(i); }

Solution

1. Step 1: Understand loop range and insertion

   We want to insert 1, 2, 3 at the end, so loop from 1 to 3 inclusive.

2. Step 2: Check each option

   A pushes 0,1,2 instead of 1,2,3.
   B assigns directly to indices 1,2,3 leaving index 0 empty.
   C uses push with i from 1 to 3, correctly adding 1,2,3.
   D loops from 1 to 2 only, missing 3.

3. Final Answer:

   for(let i = 1; i <= 3; i++) { data.push(i); } -> Option D

4. Quick Check:

   Loop 1 to 3 with push() adds correct elements [OK]

Hint: Loop from 1 to 3 and push each value [OK]

Common Mistakes:

• Using wrong loop range
• Assigning to array indices instead of push
• Starting loop at 0 instead of 1