Array Deletion at Beginning in DSA Java - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to remove the first element from the array by shifting elements left.

DSA Java

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

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

Ai + 1

Bi - 1

Cn - i

Di

Attempts:

3 left

💡 Hint

Common Mistakes

Using arr[i - 1] causes index errors.

Using arr[i] does not shift elements.

Using arr[n - i] accesses out of bounds.

To delete the first element, each element is replaced by the next element, so arr[i] = arr[i + 1].

2fill in blank

medium

Complete the code to decrease the size of the array after deletion.

DSA Java

n = [1];

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

An + 1

Bn - 1

Cn

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Increasing n instead of decreasing.

Setting n to zero resets the array incorrectly.

After deleting one element, the size n should decrease by 1.

3fill in blank

hard

Fix the error in the loop condition to avoid out-of-bounds access during deletion.

DSA Java

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

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

An

Bn + 1

Cn - 2

Dn - 1

Attempts:

3 left

💡 Hint

Common Mistakes

Using n causes index out of bounds.

Using n + 1 causes runtime errors.

The loop should run till n - 1 to avoid accessing arr[n], which is out of bounds.

4fill in blank

hard

Fill both blanks to print the array elements after deletion.

DSA Java

for (int i = 0; i < [1]; i++) {
    System.out.print(arr[[2]] + " ");
}

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

An

Bn - 1

Ci

Di + 1

Attempts:

3 left

💡 Hint

Common Mistakes

Looping till n causes printing of invalid elements.

Using arr[i + 1] skips the first element.

After deletion, print elements from index 0 to n-2 using arr[i].

5fill in blank

hard

Fill all three blanks to implement a method that deletes the first element from an array.

DSA Java

public static int deleteFirst(int[] arr, int n) {
    for (int i = 0; i < [1]; i++) {
        arr[i] = arr[[2]];
    }
    n = [3];
    return n;
}

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

An - 1

Bi + 1

Dn + 1

Attempts:

3 left

💡 Hint

Common Mistakes

Looping till n causes index errors.

Incorrectly updating n to n + 1 instead of n - 1.

Loop runs till n-1, shifting elements left by assigning arr[i] = arr[i+1], then size decreases by 1.

Practice

1. What happens to the elements of an array when you delete the first element (at the beginning)?

easy

A. All elements shift one position to the left, and the first element is removed.

B. All elements shift one position to the right, and the last element is removed.

C. The array size increases by one.

D. The array remains unchanged.

Solution

1. Step 1: Understand array deletion at beginning

   Deleting the first element means removing the element at index 0.

2. Step 2: Effect on remaining elements

   All other elements move one position left to fill the gap, reducing the array size by one.

3. Final Answer:

   All elements shift one position to the left, and the first element is removed. -> Option A

4. Quick Check:

   Delete first element = shift left [OK]

Hint: Deleting first element shifts all others left by one [OK]

Common Mistakes:

• Thinking elements shift right instead of left
• Assuming array size stays the same
• Believing the array remains unchanged

2. Which of the following Java code snippets correctly deletes the first element from an integer array arr and shifts the remaining elements left?

easy

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

B. for (int i = arr.length - 1; i > 0; i--) { arr[i] = arr[i - 1]; }

C. for (int i = 0; i < arr.length - 1; i++) { arr[i] = arr[i + 1]; }

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

Solution

1. Step 1: Identify correct loop direction and indices

   To shift elements left, start from index 0 to length-2, assigning arr[i] = arr[i+1].

2. Step 2: Check each option

   for (int i = 0; i < arr.length - 1; i++) { arr[i] = arr[i + 1]; } matches this logic; others shift right or use wrong indices causing errors.

3. Final Answer:

   for (int i = 0; i < arr.length - 1; i++) { arr[i] = arr[i + 1]; } -> Option C

4. Quick Check:

   Shift left loop: i from 0 to length-2 [OK]

Hint: Shift left by copying arr[i+1] to arr[i] in forward loop [OK]

Common Mistakes:

• Looping backwards when shifting left
• Using wrong indices causing ArrayIndexOutOfBounds
• Assigning arr[i-1] instead of arr[i+1]

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

int[] arr = {10, 20, 30, 40, 50};
for (int i = 0; i < arr.length - 1; i++) {
    arr[i] = arr[i + 1];
}
arr[arr.length - 1] = 0;
for (int num : arr) {
    System.out.print(num + " ");
}

medium

A. 20 30 40 50 0

B. 10 20 30 40 50

C. 0 10 20 30 40

D. 50 40 30 20 10

Solution

1. Step 1: Trace the shifting loop

   Each element moves left: arr[0]=20, arr[1]=30, arr[2]=40, arr[3]=50.

2. Step 2: Set last element to 0

   arr[4] is set to 0 explicitly.

3. Final Answer:

   20 30 40 50 0 -> Option A

4. Quick Check:

   Shift left + last zero = 20 30 40 50 0 [OK]

Hint: After shift, last element set to zero to fill gap [OK]

Common Mistakes:

• Forgetting to set last element to zero
• Printing original array without shift
• Confusing shift direction

4. The following code attempts to delete the first element of an array but causes an error. What is the error?

int[] arr = {1, 2, 3, 4};
for (int i = 0; i <= arr.length - 1; i++) {
    arr[i] = arr[i + 1];
}

medium

A. Logical error: elements shift right instead of left

B. ArrayIndexOutOfBoundsException at i = 3

C. Syntax error due to missing semicolon

D. No error, code runs fine

Solution

1. Step 1: Analyze loop range

   The loop runs i from 0 to arr.length - 1 (i.e., 0 to 3).

2. Step 2: Identify out-of-bounds access

   At i=3, arr[i+1] = arr[4] is accessed, which is outside array bounds causing exception.

3. Final Answer:

   ArrayIndexOutOfBoundsException at i = 3 -> Option B

4. Quick Check:

   Accessing arr[4] in length 4 array causes exception [OK]

Hint: Loop till length-2 to avoid out-of-bounds [OK]

Common Mistakes:

• Using <= instead of < in loop condition
• Ignoring array length limits
• Assuming code runs without error

5. Given an array arr = {5, 10, 15, 20, 25}, write the output after deleting the first element twice using the standard shift-left method and setting the last element to zero each time.
What is the final state of the array?

hard

A. [5, 10, 15, 20, 25]

B. [10, 15, 20, 25, 0]

C. [0, 0, 15, 20, 25]

D. [15, 20, 25, 0, 0]

Solution

1. Step 1: First deletion

   Shift left: arr becomes [10, 15, 20, 25, 0]

2. Step 2: Second deletion

   Shift left again: arr becomes [15, 20, 25, 0, 0]

3. Final Answer:

   [15, 20, 25, 0, 0] -> Option D

4. Quick Check:

   Two shifts left + zeros at end = [15, 20, 25, 0, 0] [OK]

Hint: Each deletion shifts left and adds zero at end [OK]

Common Mistakes:

• Deleting only once instead of twice
• Not setting last element to zero after shift
• Confusing order of elements after shifts