Array modification (push, pop, shift, unshift) in Ruby - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Ruby code?

Consider the following Ruby code snippet. What will be printed after all operations?

Ruby

arr = [1, 2, 3]
arr.push(4)
arr.shift
puts arr.inspect

A [4, 1, 2, 3]

B [1, 2, 3, 4]

C [2, 3, 4]

D [1, 2, 3]

💡 Hint

Remember that push adds to the end and shift removes from the start.

The array starts as [1, 2, 3]. push(4) adds 4 at the end, making it [1, 2, 3, 4]. Then shift removes the first element (1), leaving [2, 3, 4].

❓ Predict Output

intermediate

What does this Ruby code print?

Look at this code. What will be the output?

Ruby

arr = ['a', 'b', 'c']
arr.unshift('z')
arr.pop
puts arr.inspect

A ["z", "a", "b"]

B ["a", "b", "c", "z"]

C ["z", "a", "b", "c"]

D ["a", "b"]

💡 Hint

unshift adds at the start, pop removes from the end.

Starting with ['a', 'b', 'c'], unshift('z') adds 'z' at the front: ['z', 'a', 'b', 'c']. Then pop removes the last element 'c', resulting in ['z', 'a', 'b'].

❓ Predict Output

advanced

What is the final array after these operations?

Analyze the code and determine the final array content.

Ruby

arr = [10, 20, 30, 40]
arr.pop
arr.unshift(5)
arr.push(50)
arr.shift
puts arr.inspect

A [10, 20, 30, 50]

B [20, 30, 50]

C [5, 10, 20, 30]

D [5, 10, 20, 30, 50]

💡 Hint

Track each operation step-by-step.

Start: [10, 20, 30, 40]
pop removes 40 → [10, 20, 30]
unshift(5) adds 5 at front → [5, 10, 20, 30]
push(50) adds 50 at end → [5, 10, 20, 30, 50]
shift removes first element (5) → [10, 20, 30, 50]

❓ Predict Output

advanced

What error does this Ruby code raise?

Examine the code and identify the error it produces when run.

Ruby

arr = [1, 2, 3]
arr.pop(-5)
puts arr.inspect

A IndexError

B ArgumentError

C No error, outputs [1]

D TypeError

💡 Hint

Check the Ruby documentation for pop method arguments.

The pop method can take an optional argument for number of elements to remove. However, if the argument is negative, Ruby raises an ArgumentError.

🧠 Conceptual

expert

How many elements are in the array after these operations?

Given the code below, how many elements does the array contain at the end?

Ruby

arr = []
arr.unshift(1)
arr.push(2)
arr.unshift(3)
arr.pop
arr.shift
arr.push(4)
arr.shift

A 2

B 0

C 3

D 1

💡 Hint

Count carefully after each operation.

Start: []
unshift(1) → [1]
push(2) → [1, 2]
unshift(3) → [3, 1, 2]
pop removes last (2) → [3, 1]
shift removes first (3) → [1]
push(4) → [1, 4]
shift removes first (1) → [4]

Final array has 1 element.

Practice

1. Which Ruby array method adds an element to the end of the array?

easy

A. shift

B. pop

C. push

D. unshift

Solution

1. Step 1: Understand the purpose of push

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

2. Step 2: Compare with other methods

   pop removes the last element, shift removes the first, and unshift adds to the front.

3. Final Answer:

   push -> Option C

4. Quick Check:

   push adds to end [OK]

Hint: Remember: push = add end, unshift = add front [OK]

Common Mistakes:

• Confusing push with pop
• Mixing shift and unshift
• Thinking pop adds elements

2. Which of the following is the correct syntax to remove the first element from an array arr in Ruby?

easy

A. arr.shift()

B. arr.pop()

C. arr.unshift()

D. arr.push()

Solution

1. Step 1: Identify method to remove first element

   The shift method removes and returns the first element of an array.

2. Step 2: Check syntax correctness

   Calling arr.shift() correctly removes the first element.

3. Final Answer:

   arr.shift() -> Option A

4. Quick Check:

   shift removes first element [OK]

Hint: shift removes first, pop removes last [OK]

Common Mistakes:

• Using pop to remove first element
• Calling unshift to remove elements
• Forgetting parentheses

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

arr = [1, 2, 3]
arr.push(4)
arr.shift
p arr

medium

A. [1, 2, 3]

B. [1, 2, 3, 4]

C. [4, 1, 2, 3]

D. [2, 3, 4]

Solution

1. Step 1: Execute push(4) on array

   Adding 4 to the end changes array from [1, 2, 3] to [1, 2, 3, 4].

2. Step 2: Execute shift to remove first element

   Removing first element (1) results in [2, 3, 4].

3. Final Answer:

   [2, 3, 4] -> Option D

4. Quick Check:

   push adds end, shift removes front = [2, 3, 4] [OK]

Hint: push adds end, shift removes front, watch order [OK]

Common Mistakes:

• Ignoring shift effect
• Thinking push adds front
• Confusing pop with shift

4. The following Ruby code is intended to add 0 to the front of the array nums and then remove the last element. What is the error?

nums = [1, 2, 3]
nums.unshift(0)
nums.pop()

medium

A. No error; code works correctly

B. pop() should be called before unshift()

C. unshift() does not add elements to array

D. pop() removes the first element, not the last

Solution

1. Step 1: Understand unshift(0) effect

   This adds 0 to the front, changing [1, 2, 3] to [0, 1, 2, 3].

2. Step 2: Understand pop() effect

   This removes the last element (3), resulting in [0, 1, 2].

3. Final Answer:

   No error; code works correctly -> Option A

4. Quick Check:

   unshift adds front, pop removes last = correct [OK]

Hint: unshift adds front, pop removes last, order matters [OK]

Common Mistakes:

• Thinking pop removes first element
• Believing unshift does not add
• Swapping order of operations unnecessarily

5. Given the array data = [10, 20, 30], which sequence of method calls will result in [5, 10, 20]?

hard

A. data.push(5).shift()

B. data.unshift(5).pop()

C. data.shift().unshift(5)

D. data.pop().unshift(5)

Solution

1. Step 1: Apply unshift(5) to add 5 at front

   Array changes from [10, 20, 30] to [5, 10, 20, 30].

2. Step 2: Apply pop() to remove last element

   Removing last element (30) results in [5, 10, 20].

3. Final Answer:

   data.unshift(5).pop() -> Option B

4. Quick Check:

   unshift adds front, pop removes last = [5, 10, 20] [OK]

Hint: Add front with unshift, then remove last with pop [OK]

Common Mistakes:

• Using push instead of unshift
• Removing first element instead of last
• Chaining methods incorrectly