Array Deletion at Middle Index in DSA Java - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to remove the element at the middle index from the array.

DSA Java

int mid = arr.length / [1];

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A1

B2

C4

D3

Attempts:

3 left

💡 Hint

Common Mistakes

Using length / 3 instead of length / 2

Using length - 1 as middle index

To find the middle index, divide the array length by 2.

2fill in blank

medium

Complete the code to shift elements left after deleting the middle element.

DSA Java

for (int i = mid; i < arr.length - 1; i++) {
    arr[i] = arr[1];
}

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A[i + 1]

B[i - 1]

C[mid + 1]

D[mid - 1]

Attempts:

3 left

💡 Hint

Common Mistakes

Using arr[i - 1] which shifts elements incorrectly

Using fixed index instead of i + 1

After deleting the middle element, shift elements from the right to the left by one position.

3fill in blank

hard

Fix the error in the code to update the array size after deletion.

DSA Java

int newSize = arr.length [1] 1;

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A+

B*

C/

D-

Attempts:

3 left

💡 Hint

Common Mistakes

Using '+' which increases the size

Using '*' or '/' which are incorrect here

After deleting one element, the new size is original size minus one.

4fill in blank

hard

Fill both blanks to create a new array with updated size and copy elements.

DSA Java

int[] newArr = new int[[1]];
for (int i = 0; i < [2]; i++) {
    newArr[i] = arr[i];
}

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AnewSize

Barr.length

Cmid

Darr.length - 1

Attempts:

3 left

💡 Hint

Common Mistakes

Using original array length which is too large

Copying only up to mid which misses elements

The new array size is newSize, and we copy elements up to newSize.

5fill in blank

hard

Fill all three blanks to complete the method that deletes the middle element from an array.

DSA Java

public static int[] deleteMiddle(int[] arr) {
    int mid = arr.length / [1];
    for (int i = mid; i < arr.length - 1; i++) {
        arr[i] = arr[2];
    }
    int newSize = arr.length [3] 1;
    int[] newArr = new int[newSize];
    for (int i = 0; i < newSize; i++) {
        newArr[i] = arr[i];
    }
    return newArr;
}

Drag options to blanks, or click blank then click option'

A2

B[i + 1]

C-

D[i - 1]

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong index calculation for mid

Shifting elements incorrectly with arr[i - 1]

Increasing size instead of decreasing

The middle index is length divided by 2, shift elements left by assigning arr[i] = arr[i + 1], and reduce size by 1.

Practice

1. What happens when you delete the middle element from an array of size 5?
int[] arr = {10, 20, 30, 40, 50};
Delete element at index 2 (middle). What is the resulting 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 size is 5, so middle index is 2 (0-based). Element at index 2 is 30.

2. Step 2: Remove the element and shift remaining

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

3. Final Answer:

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

4. Quick Check:

   Middle element 30 removed, array shrinks by one [OK]

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

Common Mistakes:

• Not shifting elements after deletion
• Deleting wrong index (not middle)
• Leaving array size unchanged

2. Which of the following Java code snippets correctly deletes the middle element from an array arr of odd length n?

easy

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

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

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

D. for (int i = 0; i < n; i++) arr[i] = arr[i + 1];

Solution

1. Step 1: Understand the deletion index

   Middle index for odd length n is n/2 (integer division). We must shift elements after this index left.

2. Step 2: Check loop correctness

   Loop from n/2 to n-2 shifts elements left by copying arr[i+1] to arr[i]. This correctly removes middle element.

3. Final Answer:

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

4. Quick Check:

   Shift elements after middle left [OK]

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

Common Mistakes:

• Looping from 0 instead of middle index
• Shifting elements right instead of left
• Loop running out of array bounds

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

int[] arr = {5, 10, 15, 20, 25, 30, 35};
int n = arr.length;
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++) {
    System.out.print(arr[i] + " ");
}

medium

A. 5 10 15 20 25 35

B. 5 10 15 25 30 35

C. 5 10 15 20 25 30 35

D. 5 10 15 20 25 30

Solution

1. Step 1: Identify middle index and element

   Array length n=7, middle index mid=3, element at index 3 is 20.

2. Step 2: Shift elements left from middle

   Loop shifts elements from index 3 to 5 left by one: arr[3]=arr[4]=25, arr[4]=arr[5]=30, arr[5]=arr[6]=35.

3. Step 3: Decrease size and print

   n is decremented to 6, so print first 6 elements: 5 10 15 25 30 35.

4. Final Answer:

   5 10 15 25 30 35 -> Option B

5. Quick Check:

   Middle element 20 removed, array shifted left [OK]

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

Common Mistakes:

• Printing full original array length
• Not decrementing array size after deletion
• Confusing middle index calculation

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

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

medium

A. Loop should start from 0, not mid

B. Middle index calculation is wrong for odd length arrays

C. Array size n should not be decremented

D. Loop runs out of array bounds accessing arr[i+1] when i = n-1

Solution

1. Step 1: Analyze loop range and array access

   Loop runs from i = mid to i = n-1. At i = n-1, arr[i+1] = arr[n] is accessed, which is out of bounds.

2. Step 2: Correct loop boundary

   Loop should run until i < n-1 to avoid out-of-bounds access when shifting elements left.

3. Final Answer:

   Loop runs out of array bounds accessing arr[i+1] when i = n-1 -> Option D

4. Quick Check:

   Array index out of bounds error [OK]

Hint: Loop till n-1, not n, to avoid arr[i+1] error [OK]

Common Mistakes:

• Using wrong loop end condition
• Ignoring array index limits
• Incorrect middle index for even length arrays

5. Given an array arr = {2, 4, 6, 8, 10, 12} of even length 6, how do you delete the middle element(s) to keep the array balanced? Choose the correct resulting array after deleting the middle element(s).

hard

A. [2, 4, 8, 10, 12]

B. [2, 4, 6, 10, 12]

C. [2, 4, 8, 12]

D. [2, 4, 6, 8, 10]

Solution

1. Step 1: Identify middle elements for even length

   For length 6, middle indices are 2 and 3 (elements 6 and 8).

2. Step 2: Delete one or both middle elements to keep balance

   Usually, delete one middle element to keep array balanced. Deleting element at index 2 (6) shifts elements left.

3. Step 3: Resulting array after deleting element at index 2

   Array becomes [2, 4, 8, 10, 12] after shifting elements left and reducing size by one.

4. Final Answer:

   [2, 4, 8, 10, 12] -> Option A

5. Quick Check:

   Delete one middle element, shift left, size reduces [OK]

Hint: For even length, delete lower middle index element [OK]

Common Mistakes:

• Deleting both middle elements instead of one
• Deleting wrong middle index
• Not shifting elements after deletion