Array Deletion at Beginning in DSA Java - Build from Scratch

Array Deletion at Beginning

📖 Scenario: You have a list of daily tasks to complete. Sometimes, you finish the first task and want to remove it from the list to focus on the next ones.

🎯 Goal: Learn how to remove the first element from an array by shifting all other elements to the left.

📋 What You'll Learn

Create an integer array called tasks with exact values {10, 20, 30, 40, 50}

Create an integer variable called size and set it to the length of tasks

Write a loop to shift all elements in tasks one position to the left, effectively deleting the first element

Decrease size by 1 to reflect the new array size

Print the elements of tasks from index 0 to size - 1 separated by spaces

💡 Why This Matters

🌍 Real World

Managing task lists or queues where the first item is completed and removed.

💼 Career

Understanding array manipulation is fundamental for software development and data handling.

1

Create the initial array

Create an integer array called tasks with these exact values: {10, 20, 30, 40, 50}

DSA Java

# Create the integer array tasks with values {10, 20, 30, 40, 50}
// Your code here

Hint

Use int[] tasks = {10, 20, 30, 40, 50}; to create the array.

2

Set the size variable

Create an integer variable called size and set it to the length of the tasks array

DSA Java

int[] tasks = {10, 20, 30, 40, 50};
// Create an integer variable size and set it to tasks.length
// Your code here

Hint

Use int size = tasks.length; to get the array length.

3

Shift elements to delete the first element

Write a for loop with variable i from 0 to size - 2 to shift each element in tasks one position to the left by assigning tasks[i] = tasks[i + 1]. Then decrease size by 1.

DSA Java

int[] tasks = {10, 20, 30, 40, 50};
int size = tasks.length;
// Shift elements left to delete the first element
// Your code here

Hint

Use a for loop to move each element left and then reduce size by 1.

4

Print the updated array

Use a for loop with variable i from 0 to size - 1 to print each element of tasks separated by spaces on one line.

DSA Java

int[] tasks = {10, 20, 30, 40, 50};
int size = tasks.length;
for (int i = 0; i < size - 1; i++) {
    tasks[i] = tasks[i + 1];
}
size--;
// Print elements from index 0 to size - 1 separated by spaces
// Your code here

Hint

Use a for loop and System.out.print() to show the updated array.

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