Array Deletion at End in DSA Go - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does 'Array Deletion at End' mean?

It means removing the last element from an array, reducing its size by one.

beginner

In Go, how do you remove the last element from a slice named arr?

You can remove the last element by slicing: arr = arr[:len(arr)-1].

beginner

Why is deleting at the end of an array efficient?

Because it does not require shifting elements; just reducing the length is enough.

intermediate

What happens if you try to delete an element from an empty array?

It causes an error or panic because there is no element to remove.

beginner

Show the Go code snippet to delete the last element from a slice and print the result.

package main
import "fmt"
func main() {
  arr := []int{1, 2, 3, 4}
  arr = arr[:len(arr)-1]
  fmt.Println(arr) // Output: [1 2 3]
}

What is the result of deleting the last element from array [5, 6, 7]?

A [5, 7]

B [6, 7]

C [5, 6]

D [5, 6, 7]

Deleting the last element removes 7, leaving [5, 6].

In Go, which expression removes the last element from slice arr?

A arr = arr[len(arr):]

B arr = arr[1:]

C arr = arr[1:len(arr)]

D arr = arr[:len(arr)-1]

Slicing up to len(arr)-1 removes the last element.

What happens if you delete the last element from an empty array?

A Array becomes empty again

B Error or panic occurs

C Array adds a new element

D Nothing happens

You cannot remove elements from an empty array; it causes an error.

Why is deleting at the end of an array faster than deleting at the start?

A No elements need to be moved

B It uses more memory

C It requires sorting

D It needs extra copying

Deleting at the end just shortens the array; no shifting needed.

After deleting the last element from [10, 20, 30, 40], what is the new array?

A [10, 20, 30]

B [20, 30, 40]

C [10, 20, 40]

D [10, 20, 30, 40]

The last element 40 is removed, leaving [10, 20, 30].

Explain how to delete the last element from an array or slice and why it is efficient.

Think about how arrays store elements in order.

Describe what happens if you try to delete the last element from an empty array and how to avoid errors.

Consider what happens when there is nothing to remove.

Practice

1. What happens when you delete an element from the end of an array in Go?

easy

A. The last element is removed and the array size decreases by one.

B. The first element is removed and the array size decreases by one.

C. The array size stays the same but the last element becomes zero.

D. The array is completely cleared and becomes empty.

Solution

1. Step 1: Understand array deletion at end

   Deleting at the end means removing the last element only, not the first or all.

2. Step 2: Effect on array size

   After removal, the array size decreases by one because one element is gone.

3. Final Answer:

   The last element is removed and the array size decreases by one. -> Option A

4. Quick Check:

   Deleting end element reduces size by one [OK]

Hint: Deleting at end removes last element and shrinks array [OK]

Common Mistakes:

• Thinking first element is removed
• Assuming array size stays same
• Believing array clears completely

2. Which of the following Go code snippets correctly deletes the last element from a slice named arr?

easy

A. arr = arr[len(arr):]

B. arr = arr[:len(arr)-1]

C. arr = arr[1:]

D. arr = arr[:len(arr)+1]

Solution

1. Step 1: Understand slice slicing syntax

   To remove last element, slice up to length minus one: arr[:len(arr)-1].

2. Step 2: Check other options

   arr[len(arr):] results in empty slice, arr[1:] removes first element, arr[:len(arr)+1] causes runtime error.

3. Final Answer:

   arr = arr[:len(arr)-1] -> Option B

4. Quick Check:

   Slice up to len-1 removes last element [OK]

Hint: Use arr[:len(arr)-1] to drop last element [OK]

Common Mistakes:

• Using arr[1:] removes first element
• Using arr[len(arr):] gives empty slice
• Using arr[:len(arr)+1] causes error

3. What is the output of this Go code?

arr := []int{10, 20, 30, 40}
arr = arr[:len(arr)-1]
fmt.Println(arr)

medium

A. [10 20 30 40]

B. []

C. [10 20 30]

D. [20 30 40]

Solution

1. Step 1: Initial array and slicing

   arr starts as [10 20 30 40]. Slicing arr[:len(arr)-1] means arr[:3].

2. Step 2: Result after slicing

   arr[:3] gives first three elements: [10 20 30].

3. Final Answer:

   [10 20 30] -> Option C

4. Quick Check:

   Slice up to len-1 excludes last element [OK]

Hint: Slicing arr[:len(arr)-1] drops last element [OK]

Common Mistakes:

• Expecting last element to remain
• Confusing arr[1:] with arr[:len(arr)-1]
• Thinking output is empty slice

4. Identify the error in this Go code that tries to delete the last element from arr:

arr := []int{1, 2, 3}
arr = arr[:len(arr)]
fmt.Println(arr)

medium

A. It deletes all elements making the array empty.

B. It causes a runtime panic due to invalid slice bounds.

C. It deletes the first element instead of the last.

D. It does not delete any element; array remains unchanged.

Solution

1. Step 1: Analyze slicing bounds

   arr[:len(arr)] means slice from start to full length, so no element is removed.

2. Step 2: Effect on array

   Since slice covers entire array, arr remains [1 2 3] unchanged.

3. Final Answer:

   It does not delete any element; array remains unchanged. -> Option D

4. Quick Check:

   Slicing arr[:len(arr)] keeps full array [OK]

Hint: arr[:len(arr)] keeps full array, no deletion [OK]

Common Mistakes:

• Assuming last element is deleted
• Expecting runtime error
• Thinking first element is removed

5. Given a slice arr := []int{5, 10, 15, 20, 25}, write the Go code to delete the last two elements and print the resulting slice.

hard

A. arr = arr[:len(arr)-2]
fmt.Println(arr)

B. arr = arr[2:]
fmt.Println(arr)

C. arr = arr[:len(arr)-1]
fmt.Println(arr)

D. arr = arr[1:len(arr)-1]
fmt.Println(arr)

Solution

1. Step 1: Understand deletion of last two elements

   To remove last two elements, slice up to length minus two: arr[:len(arr)-2].

2. Step 2: Apply slicing and print

   arr[:3] gives [5 10 15]. Printing arr shows these three elements.

3. Final Answer:

   arr = arr[:len(arr)-2] fmt.Println(arr) -> Option A

4. Quick Check:

   Slice up to len-2 removes last two elements [OK]

Hint: Use arr[:len(arr)-2] to remove last two elements [OK]

Common Mistakes:

• Using arr[2:] removes first two elements
• Removing only last element instead of two
• Incorrect slice bounds causing errors