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 after deleting the middle element from the array?

DSA C

#include <stdio.h>

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

int main() {
    int arr[] = {10, 20, 30, 40, 50};
    int n = 5;
    deleteMiddle(arr, &n);
    for (int i = 0; i < n; i++) {
        printf("%d ", arr[i]);
    }
    return 0;
}

A 10 20 30 50

B 10 20 40 50

C 20 30 40 50

D 10 20 30 40 50

💡 Hint

Remember that deleting the middle element means shifting elements after the middle one to the left.

The middle index for an array of size 5 is 2 (0-based). The element at index 2 (30) is removed, and elements after it (40, 50) shift left. The new array is 10, 20, 40, 50.

❓ Predict Output

intermediate

Resulting array size after middle deletion

What is the size of the array after deleting the middle element using the code below?

DSA C

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

int main() {
    int arr[] = {1, 2, 3, 4, 5, 6};
    int n = 6;
    deleteMiddle(arr, &n);
    printf("%d", n);
    return 0;
}

A 3

B 6

C 5

D 4

💡 Hint

Deleting one element reduces the size by one.

Initially, the array size is 6. After deleting the middle element (index 3), the size decreases by 1 to 5.

🔧 Debug

advanced

Identify the error in middle deletion code

What error will occur when running this code to delete the middle element?

DSA C

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

int main() {
    int arr[] = {5, 10, 15, 20, 25};
    int n = 5;
    deleteMiddle(arr, &n);
    for (int i = 0; i < n; i++) {
        printf("%d ", arr[i]);
    }
    return 0;
}

A Runtime error due to out-of-bounds access

B Runs correctly and outputs: 5 10 20 25

C Runs but outputs: 5 10 15 20 25

D Compilation error due to syntax

💡 Hint

Check the loop boundary and array indexing carefully.

The loop runs from mid to n, and accesses arr[i + 1]. When i = n - 1, arr[i + 1] accesses arr[n], which is out of bounds causing runtime error.

❓ Predict Output

advanced

Output after deleting middle element from even-sized array

What is the output of this code after deleting the middle element from an even-sized array?

DSA C

#include <stdio.h>

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

int main() {
    int arr[] = {2, 4, 6, 8, 10, 12};
    int n = 6;
    deleteMiddle(arr, &n);
    for (int i = 0; i < n; i++) {
        printf("%d ", arr[i]);
    }
    return 0;
}

A 2 4 8 10 12

B 2 4 6 8 10 12

C 2 4 6 10 12

D 4 6 8 10 12

💡 Hint

For even length, middle is the lower middle index.

For n=6, mid = (6-1)/2 = 2. Element at index 2 (6) is deleted. Elements after index 2 shift left. Result: 2 4 8 10 12.

🧠 Conceptual

expert

Time complexity of deleting middle element in array

What is the time complexity of deleting the middle element from an array of size n by shifting elements?

A O(n^2) - Quadratic time

B O(log n) - Logarithmic time

C O(1) - Constant time

D O(n) - Linear time

💡 Hint

Consider how many elements need to be moved after deletion.

Deleting the middle element requires shifting roughly half the elements, which is proportional to n, so time complexity is O(n).

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. [10, 20, 40, 50]

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

C. [10, 20, 30, 50]

D. [20, 30, 40, 50]

Solution

1. Step 1: Identify the middle index and element

   The array has 5 elements, so the middle index is 2 (0-based). 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 A

4. Quick Check:

   Middle element removed, array size reduced by 1 [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 > 0; i--) arr[i] = arr[i - 1]; n--;

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

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

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

Solution

1. Step 1: Identify the middle index and loop direction

   The middle index is n/2 (integer division). To delete, shift elements after middle left.

2. Step 2: Check loop correctness

   for (int i = n/2; i < n - 1; i++) arr[i] = arr[i + 1]; n--; shifts elements from middle to end left by one, then reduces size. This is correct.

3. Final Answer:

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

4. Quick Check:

   Shift elements after middle left [OK]

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

Common Mistakes:

• Shifting elements before middle
• Looping in wrong direction
• Not reducing array size

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++) {
    printf("%d ", arr[i]);
}

medium

A. 5 10 15 20 25 30

B. 5 10 15 20 30

C. 5 10 15 25 30

D. 5 10 20 25 30

Solution

1. Step 1: Calculate middle index and deletion

   n=6, mid=3. Element at index 3 is 20. It will be deleted.

2. Step 2: Shift elements after index 3 left by one

   arr[3] = arr[4] (25), arr[4] = arr[5] (30), n becomes 5.

3. Step 3: Print updated array

   Elements: 5, 10, 15, 25, 30

4. Final Answer:

   5 10 15 25 30 -> Option C

5. Quick Check:

   Deleted middle element, shifted right elements left [OK]

Hint: Delete middle, shift right elements left, print first n-1 elements [OK]

Common Mistakes:

• Printing original array size
• Not shifting elements correctly
• Deleting wrong index

4. Find the error in this code snippet that deletes the middle element from an array arr of size n:

int mid = n / 2;
for (int i = 0; i < mid; i++) {
    arr[i] = arr[i + 1];
}
n--;

medium

A. Middle index calculation is wrong, should be (n-1)/2

B. Loop shifts elements before middle, should shift after middle

C. Array size decrement should be before loop

D. No error, code is correct

Solution

1. Step 1: Analyze loop range and shifting direction

   The loop runs from 0 to mid-1, shifting elements before middle left, which is incorrect.

2. Step 2: Correct shifting after middle index

   To delete middle element, shift elements from middle index to end left by one, not before middle.

3. Final Answer:

   Loop shifts elements before middle, should shift after middle -> Option B

4. Quick Check:

   Shift elements after middle, not before [OK]

Hint: Shift elements after middle, not before [OK]

Common Mistakes:

• Shifting elements before middle
• Wrong loop boundaries
• Not reducing array size

5. Given an array arr of size n where n is even, write the steps to delete the middle two elements and shift the rest. What will be the new array after deleting middle elements from {1, 2, 3, 4, 5, 6}?

hard

A. [1, 2, 5, 6]

B. [1, 2, 3, 6]

C. [1, 2, 4, 5, 6]

D. [1, 3, 4, 5, 6]

Solution

1. Step 1: Identify middle two indices for even-sized array

   For n=6, middle two indices are 2 and 3 (0-based), elements 3 and 4.

2. Step 2: Delete these two elements and shift remaining elements left

   Shift elements from index 4 and 5 left by two positions: 5 moves to index 2, 6 moves to index 3. Reduce size by 2.

3. Step 3: New array after deletion

   Array becomes [1, 2, 5, 6]

4. Final Answer:

   [1, 2, 5, 6] -> Option A

5. Quick Check:

   Delete two middle elements, shift right elements left by two [OK]

Hint: Delete two middles, shift right elements left by two [OK]

Common Mistakes:

• Deleting only one middle element
• Shifting elements incorrectly
• Not reducing array size by two