Array Insertion at End in DSA Typescript - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does 'Array Insertion at End' mean?

It means adding a new item to the last position of an array, making the array one item longer.

beginner

How do you insert an element at the end of an array in TypeScript?

Use the push() method. For example, arr.push(value) adds value to the end of arr.

beginner

What happens to the array length after insertion at the end?

The array length increases by one because a new element is added at the last position.

intermediate

What is the time complexity of inserting an element at the end of an array in TypeScript?

It is usually O(1), meaning it takes constant time because the element is added directly at the end.

intermediate

Can you insert multiple elements at the end of an array at once? How?

Yes, use push() with multiple arguments, like arr.push(val1, val2, val3) to add several elements at the end.

Which method adds an element to the end of an array in TypeScript?

A push()

B pop()

C shift()

D unshift()

push() adds elements to the end. pop() removes from the end. shift() removes from the start. unshift() adds to the start.

What is the length of array [1, 2, 3] after arr.push(4)?

A Undefined

B 3

C 5

D 4

After pushing 4, the array becomes [1, 2, 3, 4] with length 4.

What is the time complexity of inserting an element at the end of a TypeScript array?

A O(n)

B O(1)

C O(log n)

D O(n^2)

Insertion at the end is usually constant time, O(1), because it adds directly at the last position.

Which of these will add multiple elements at the end of an array?

A arr.push(5, 6, 7)

B arr.pop(5, 6, 7)

C arr.shift(5, 6, 7)

D arr.unshift(5, 6, 7)

push() can take multiple arguments to add many elements at once.

If you want to add an element at the start of an array, which method should you use instead of push()?

A pop()

B shift()

C unshift()

D slice()

unshift() adds elements at the start of the array.

Explain how to insert an element at the end of an array in TypeScript and what happens to the array length.

Think about the method that adds items to the end and how array size changes.

Describe the time complexity of inserting an element at the end of an array and why it is efficient.

Consider how the array stores elements and how adding at the end works.

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