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

Recall & Review

beginner

What does 'Array Insertion at End' mean?

It means adding a new element to the last position of an array, increasing its size by one.

beginner

In Go, what happens if you try to insert an element at the end of a fixed-size array?

You cannot add elements beyond the fixed size. You must use a slice to insert at the end dynamically.

beginner

How do slices help with insertion at the end in Go?

Slices are dynamic and can grow. You can use the built-in append() function to add elements at the end easily.

intermediate

What is the time complexity of inserting an element at the end of a slice in Go?

Usually O(1) amortized, because append adds at the end. Sometimes it can be O(n) if the slice needs to grow its capacity.

beginner

Show a simple Go code snippet to insert an element at the end of a slice.

numbers := []int{1, 2, 3} numbers = append(numbers, 4) // Now numbers is [1, 2, 3, 4]

Which Go data structure allows easy insertion at the end?

A Struct

B Fixed-size array

C Map

D Slice

Slices are dynamic and support append to add elements at the end.

What function is used to insert an element at the end of a slice in Go?

A insert()

B append()

C push()

D add()

The built-in append() function adds elements at the end of a slice.

What happens if a slice's capacity is full when you append a new element?

A The slice automatically grows its capacity

B The element is ignored

C The program crashes

D You must manually increase capacity

Go automatically grows the slice capacity when needed during append.

Can you insert an element at the end of a fixed-size array in Go?

A Yes, always

B Only if the array is empty

C No, arrays have fixed size

D Only with a special function

Arrays have fixed size and cannot grow, so insertion at the end is not possible.

What is the time complexity of appending an element to a slice when capacity is sufficient?

A O(1)

B O(log n)

C O(n)

D O(n^2)

Appending is O(1) when capacity is enough, as it just adds the element at the end.

Explain how to insert an element at the end of an array or slice in Go.

Think about fixed size vs dynamic size and the append function.

Describe what happens internally when you append an element to a slice that has no extra capacity.

Consider how Go manages slice growth behind the scenes.

Practice

1. What happens when you insert an element at the end of a fixed-size array in Go?

easy

A. You cannot insert because arrays have fixed size

B. The element replaces the first element

C. The element is added and array size increases automatically

D. The array is converted to a slice automatically

Solution

1. Step 1: Understand Go array size

   Arrays in Go have a fixed size defined at declaration and cannot grow.

2. Step 2: Effect of insertion at end

   Since size is fixed, you cannot add new elements beyond the declared size.

3. Final Answer:

   You cannot insert because arrays have fixed size -> Option A

4. Quick Check:

   Fixed size array = no insertion beyond size [OK]

Hint: Arrays have fixed size; no automatic growth on insertion [OK]

Common Mistakes:

• Thinking arrays can grow automatically
• Confusing arrays with slices
• Assuming insertion replaces last element

2. Which of the following is the correct way to append an element 10 to a slice named nums in Go?

easy

A. nums = nums + 10

B. nums.append(10)

C. append(nums, 10)

D. nums = append(nums, 10)

Solution

1. Step 1: Recall Go slice append syntax

   In Go, append returns a new slice with the element added, so assignment is needed.

2. Step 2: Check each option

   nums = append(nums, 10) correctly assigns the result of append to nums. Others are invalid syntax or missing assignment.

3. Final Answer:

   nums = append(nums, 10) -> Option D

4. Quick Check:

   Use append with assignment to add element [OK]

Hint: Always assign append result back to slice variable [OK]

Common Mistakes:

• Not assigning append result back
• Using method call syntax like nums.append()
• Trying to add with + operator

3. What is the output of the following Go code?

nums := []int{1, 2, 3}
nums = append(nums, 4)
fmt.Println(nums)

medium

A. [1 2 3]

B. [4 1 2 3]

C. [1 2 3 4]

D. Compilation error

Solution

1. Step 1: Understand initial slice and append

   nums starts as [1 2 3]. append(nums, 4) adds 4 at the end.

2. Step 2: Print the updated slice

   After append, nums becomes [1 2 3 4], which is printed.

3. Final Answer:

   [1 2 3 4] -> Option C

4. Quick Check:

   Appending 4 adds it at end [OK]

Hint: append adds element at end, print shows updated slice [OK]

Common Mistakes:

• Expecting original slice without new element
• Thinking append adds at start
• Confusing slice with array syntax

4. Identify the error in the following Go code that tries to insert 5 at the end of an array:

arr := [3]int{1, 2, 3}
arr = append(arr, 5)
fmt.Println(arr)

medium

A. Cannot use append on array; append works only on slices

B. Array size is too small; must declare larger array

C. Missing import for fmt package

D. Syntax error in array declaration

Solution

1. Step 1: Check type of arr

   arr is declared as an array [3]int, which has fixed size and no append method.

2. Step 2: Understand append usage

   append works only on slices, not arrays. Using append on array causes error.

3. Final Answer:

   Cannot use append on array; append works only on slices -> Option A

4. Quick Check:

   append requires slice, not array [OK]

Hint: append works only on slices, not fixed-size arrays [OK]

Common Mistakes:

• Trying to append to fixed-size array
• Ignoring difference between array and slice
• Assuming append auto-converts array to slice

5. Given a slice data := []int{2, 4, 6}, which code snippet correctly inserts the value 8 at the end and then doubles all elements?

hard

A. data = append(data, 8)
for _, v := range data {
v *= 2
}
fmt.Println(data)

B. data = append(data, 8)
for i := range data {
data[i] *= 2
}
fmt.Println(data)

C. data = append(data, 8)
for i := 0; i < len(data); i++ {
data[i] = data[i] + 2
}
fmt.Println(data)

D. data = append(data, 8)
for i := range data {
data[i] = data[i] / 2
}
fmt.Println(data)

Solution

1. Step 1: Append 8 to slice

   data = append(data, 8) adds 8 at the end, making data [2 4 6 8].

2. Step 2: Double each element correctly

   Using for i := range data and data[i] *= 2 doubles each element in place.

3. Step 3: Check other options

   data = append(data, 8) for _, v := range data { v *= 2 } fmt.Println(data) doubles copy of value, not original slice. Options C and D do wrong math.

4. Final Answer:

   data = append(data, 8) for i := range data { data[i] *= 2 } fmt.Println(data) -> Option B

5. Quick Check:

   Append then modify elements by index [OK]

Hint: Modify slice elements by index, not by value copy [OK]

Common Mistakes:

• Modifying value copy in range instead of slice element
• Using wrong arithmetic operation
• Not assigning append result back