Array Deletion at Middle Index in DSA C++ - Practice Problems & Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output after deleting middle element from array

What is the output of the following C++ code that deletes the middle element from an array?

DSA C++

int arr[] = {10, 20, 30, 40, 50};
int n = 5;
int mid = n / 2;
for (int i = mid; i < n - 1; i++) {
    arr[i] = arr[i + 1];
}
n--;
for (int i = 0; i < n; i++) {
    std::cout << arr[i] << " ";
}

A 10 20 40 50

B 10 20 30 40 50

C 10 20 30 50

D 20 30 40 50

💡 Hint

Remember that deleting the middle element shifts all elements after it one position left.

The middle index is 2 (0-based). The element 30 at index 2 is removed. Elements after index 2 shift left, so 40 moves to index 2, 50 to index 3. The new array size is 4.

❓ Predict Output

intermediate

Resulting array after middle deletion with even length

What is the output of this C++ code deleting the middle element from an even-length array?

DSA C++

int arr[] = {5, 15, 25, 35, 45, 55};
int n = 6;
int mid = n / 2;
for (int i = mid; i < n - 1; i++) {
    arr[i] = arr[i + 1];
}
n--;
for (int i = 0; i < n; i++) {
    std::cout << arr[i] << " ";
}

A 5 15 25 45 55

B 5 15 25 35 45 55

C 5 15 35 45 55

D 5 15 25 35 55

💡 Hint

For even length, middle index is n/2, which is 3 here (0-based).

Middle index is 3, element 35 is removed. Elements after index 3 shift left: 45 moves to index 3, 55 to index 4. New size is 5.

🔧 Debug

advanced

Identify the bug in middle deletion code

What error will this code produce when deleting the middle element from an array?

DSA C++

int arr[] = {1, 2, 3, 4};
int n = 4;
int mid = n / 2;
for (int i = mid; i < n - 1; i++) {
    arr[i] = arr[i + 1];
}
n--;
for (int i = 0; i < n; i++) {
    std::cout << arr[i] << " ";
}

A Compilation error: invalid loop condition

B Runs correctly and outputs: 1 2 4

C Runtime error: accessing out-of-bounds element

D Outputs: 1 2 3 4

💡 Hint

Check the loop condition and array indexing carefully.

The original loop condition was incorrect and caused out-of-bounds access. It has been corrected to i < n - 1 to avoid accessing arr[n].

🧠 Conceptual

advanced

Effect of deleting middle element on array size

If you delete the middle element from an array of size n, what will be the size of the array afterwards?

A n

B n - 1

C n + 1

D Depends on whether n is even or odd

💡 Hint

Deleting one element reduces the total count by one.

Removing one element from an array reduces its size by exactly one, regardless of n being even or odd.

🚀 Application

expert

Final array state after multiple middle deletions

Given the array and code below, what is the final printed array after deleting the middle element twice in a row?

DSA C++

int arr[] = {2, 4, 6, 8, 10, 12, 14};
int n = 7;
for (int count = 0; count < 2; count++) {
    int mid = n / 2;
    for (int i = mid; i < n - 1; i++) {
        arr[i] = arr[i + 1];
    }
    n--;
}
for (int i = 0; i < n; i++) {
    std::cout << arr[i] << " ";
}

A 2 4 6 8 12 14

B 2 4 6 8 10 12

C 2 4 6 10 12 14

D 2 4 6 12 14

💡 Hint

Delete middle element once, then again on the smaller array.

First deletion removes element at index 3 (8). Array becomes {2,4,6,10,12,14}, size 6. Second deletion removes element at index 3 (10). Array becomes {2,4,6,12,14}, size 5. Final output: 2 4 6 12 14

Practice

1. What happens when you delete the middle element from an array of size 5?
int arr[5] = {10, 20, 30, 40, 50};
Delete the element at index 2 (middle). What is the new array?

easy

A. [20, 30, 40, 50]

B. [10, 20, 30, 40, 50]

C. [10, 20, 30, 50]

D. [10, 20, 40, 50]

Solution

1. Step 1: Identify the middle index and element

   The array size is 5, so middle index is 2. The element at index 2 is 30.

2. Step 2: Delete the middle element and shift remaining elements

   Remove 30, then shift elements after index 2 left by one: 40 moves to index 2, 50 moves to index 3.

3. Final Answer:

   [10, 20, 40, 50] -> Option D

4. Quick Check:

   Deleted middle element 30, shifted left [OK]

Hint: Remove middle, shift right elements left by one [OK]

Common Mistakes:

• Not shifting elements after deletion
• Deleting wrong index
• Leaving array size unchanged

2. Which of the following C++ code snippets correctly deletes the middle element from an array arr of size n?

easy

A. for(int i = n/2; i < n-1; i++) arr[i] = arr[i+1]; n--;

B. for(int i = 0; i < n/2; i++) arr[i] = arr[i+1]; n--;

C. arr[n/2] = 0; n--;

D. for(int i = n-1; i > n/2; i--) arr[i] = arr[i-1]; n--;

Solution

1. Step 1: Understand deletion logic

   To delete middle element at index n/2, shift all elements after it one position left.

2. Step 2: Check each code snippet

   for(int i = n/2; i < n-1; i++) arr[i] = arr[i+1]; n--; correctly shifts elements from middle to end left by one and reduces size. Others either shift wrong elements or just set zero without shifting.

3. Final Answer:

   for(int i = n/2; i < n-1; i++) arr[i] = arr[i+1]; n--; -> Option A

4. Quick Check:

   Shift elements after middle left [OK]

Hint: Shift elements from middle index to end left [OK]

Common Mistakes:

• Shifting elements before middle index
• Not reducing array size
• Assigning zero instead of shifting

3. What is the output of the following C++ code?

int arr[6] = {5, 10, 15, 20, 25, 30};
int n = 6;
int mid = n / 2;
for(int i = mid; i < n - 1; i++) {
  arr[i] = arr[i + 1];
}
n--;
for(int i = 0; i < n; i++) {
  std::cout << arr[i] << " ";
}

medium

A. 5 10 15 25 30

B. 5 10 15 20 25 30

C. 5 10 15 20 30

D. 5 10 20 25 30

Solution

1. Step 1: Calculate middle index and delete element

   n=6, mid=3. Element at index 3 is 20. We delete 20 by shifting elements after index 3 left.

2. Step 2: Shift elements and print array

   Shift arr[3]=arr[4]=25, arr[4]=arr[5]=30. New array: 5,10,15,25,30. Size reduced to 5.

3. Final Answer:

   5 10 15 25 30 -> Option A

4. Quick Check:

   Deleted 20, shifted left [OK]

Hint: Shift elements after middle left, reduce size by one [OK]

Common Mistakes:

• Not reducing array size
• Printing old array size
• Not shifting elements correctly

4. Find the error in this code that tries to delete the middle element from array arr of size n:

int mid = n / 2;
for(int i = mid; i <= n - 1; i++) {
  arr[i] = arr[i + 1];
}
n--;

medium

A. Array size n should not be decremented

B. Middle index calculation is wrong

C. Loop condition should be i < n - 1, not i <= n - 1

D. Loop should start from 0, not mid

Solution

1. Step 1: Analyze loop range for shifting elements

   The loop runs from mid to n-1 inclusive, so arr[i+1] accesses arr[n], which is out of bounds.

2. Step 2: Correct loop condition

   Loop should run while i < n-1 to avoid accessing beyond array size.

3. Final Answer:

   Loop condition should be i < n - 1, not i <= n - 1 -> Option C

4. Quick Check:

   Prevent out-of-bounds by correct loop limit [OK]

Hint: Loop till one before last index to avoid overflow [OK]

Common Mistakes:

• Using <= instead of < in loop condition
• Not decrementing array size
• Wrong middle index calculation

5. Given an array arr of size n, write the logic to delete the middle element and return the new array size. What will be the size after deletion if n is even?
Choose the correct approach.

hard

A. Delete element at index (n-1)/2, shift elements left, new size = n - 1

B. Delete element at index n/2, shift elements left, new size = n - 1

C. Delete element at index n/2, no shifting needed, new size = n - 1

D. Delete element at index n/2 - 1, shift elements left, new size = n - 1

Solution

1. Step 1: Understand middle index for even-sized array

   In standard array operations, middle index is n/2 (integer division), consistent with odd sizes.

2. Step 2: Delete element at n/2 and shift elements left

   Remove element at index n/2, shift all elements after it left by one, reduce size by 1.

3. Final Answer:

   Delete element at index n/2, shift elements left, new size = n - 1 -> Option B

4. Quick Check:

   Middle index = n/2 for even n [OK]

Hint: Use n/2 as middle index regardless of parity [OK]

Common Mistakes:

• Deleting lower middle index (n/2 - 1) for even n
• Not shifting elements after deletion
• Not reducing array size