Arrays: Practice Problems III

Suppose you have a list of things you need to buy at the grocery store, and you have noted these items on a piece of paper. The list is:

• Apple
• Banana
• Bread
• Milk

This list is like an array where each item is an element, and the order represents the index. 

Let's say we want to insert Eggs at the 3rd position now.

To achieve this, we will follow these steps:

1. Create a new array with a size one greater than the previous one.
2. Copy all the elements from the previous to this new array up to the position provided in the input.
3. Next, insert the element to be inserted (in this case, Eggs).
4. Finally, copy the rest of the elements from the previous array to the new array, one by one.

After following these steps, we can successfully insert an element into the array at a particular position.

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        // Input size of the array
        Scanner scanner = new Scanner(System.in);
        System.out.println("Enter size of the array: ");
        int size = scanner.nextInt();
		int [] arr = new int[size];

        // Input elements in array
        System.out.println("Enter elements in array: ");
        for (int i = 0; i < size; i++) {
            arr[i] = scanner.nextInt();
        }

        // Input new element and position to insert
        System.out.println("Enter element to insert: ");
        int num = scanner.nextInt();
        System.out.println("Enter the element position: ");
        int pos = scanner.nextInt();

        // If position of element is not valid
        if (pos > size + 1 || pos <= 0) {
            System.out.printf("Invalid position! Please enter position between 1 to %d\n", size + 1);
        } else {
			//Creating new array with size + 1
            int[] newArr = new int[size + 1];

			//Copy elements till position
			for(int i = 0; i < pos - 1; i++){
				newArr[i] = arr[i];
			}

			//Inserting the new element
			newArr[pos - 1] = num;

			//Copying the rest elements
			for(int i = pos; i <= size; i++){
				newArr[i] = arr[i - 1];
			}

            // Print array after insert operation
            System.out.print("Array elements after insertion: ");
            for (int i = 0; i <= size; i++) {
                System.out.print(newArr[i] + " ");
            }
        }

        scanner.close();
    }
}

Use the grocery list we made in the previous problem. Let's say we don't want to buy breads now. Don't just strike the item XD!

Think of the list in terms of array. We can also create a new list but attempt to do so without creating a new array.

All we have to do is move the things from the specified position one place to the left of where they are now.

1. Use the element at index "position" to begin the iteration.
2. Add the value of the current item to the preceding element's.

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        // Input size and elements in array
        Scanner scanner = new Scanner(System.in);
        System.out.println("Enter size of the array: ");
        int size = scanner.nextInt();

		//Creating the array
		int[] arr = new int[size];
        System.out.println("Enter elements in array: ");
        for (int i = 0; i < size; i++) {
            arr[i] = scanner.nextInt();
        }

        // Input element position to delete
        System.out.println("Enter the element position to delete: ");
        int pos = scanner.nextInt();

        // Check for invalid delete position
        if (pos <= 0 || pos > size) {
            System.out.printf("Invalid position! Please enter position between 1 to %d", size);
        } else {
            // Copy next element value to current element
            for (int i = pos - 1; i < size - 1; i++) {
                arr[i] = arr[i + 1];
            }

            // Decrement array size by 1
            size--;

            // Print array after deletion
            System.out.print("\nElements of array after delete are: ");
            for (int i = 0; i < size; i++) {
                System.out.printf("%d\t", arr[i]);
            }
        }

        scanner.close();
    }
}

Hints? Who needs them? No hints required; you've got this!"

1. Firstly, input the original array as usual.
2. Now, since we need to copy the elements to another array, declare another array of same size.
3. Iterate through the original array and copy elements one by one to the final array.
4. That's it! Print the arrays to check the contents of the array.

import java.util.Scanner;
public class CopyArray {
    public static void main(String[] args) {
        // Input size of the array
        Scanner scanner = new Scanner(System.in);
        int size = scanner.nextInt();
        
        //Declare the array
        int[] source = new int[size];
        int[] dest = new int[size];
        
        // Input array elements
        for (int i = 0; i < size; i++) {
            source[i] = scanner.nextInt();
        }

       // Copy all elements from source array to dest array
        for (int i = 0; i < size; i++) {
            dest[i] = source[i];
        }

        // Print all elements of source array
        System.out.print("Array1: ");
        for (int i = 0; i < size; i++) {
            System.out.print(source[i] + "\t");
        }
        
        System.out.println();
        
        // Print all elements of dest array
        System.out.print("Array2: ");
        for (int i = 0; i < size; i++) {
            System.out.print(dest[i] + "\t");
        }
        scanner.close();
    }
}

Could you please once check if all the items in our grocery list are unique?

How did you do that? You must have started with the first item, checked it with every other item. If it does not match with any other item, it is unique. Right?

We need to apply the same concept here.

1. Iterate through each element in the array using a loop.
2. For each element at position i, set a boolean variable isUnique to true, considering that the element is unique initially.
3. Use another loop to compare the element at position i with all other elements in the array at different positions (j).
4. If a matching element is found at a different position, set isUnique to false and break out of the loop. That means the element is not unique.
5. If isUnique is still true after the inner loop, print the element at position i as it is unique.

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        // Input size of array and elements in array
        Scanner scanner = new Scanner(System.in);
        System.out.println("Enter size of array: ");
        int size = scanner.nextInt();

		// Creating array
		int[] arr = new int[size];
        System.out.println("Enter elements in array: ");
        for (int i = 0; i < size; i++) {
            arr[i] = scanner.nextInt();
        }

        // Print all unique elements of array
        System.out.println("Unique elements in the array are: ");
        for (int i = 0; i < size; i++) {
            boolean isUnique = true;
			// Checking with all elements of the array
            for (int j = 0; j < size; j++) {
				// Since both the elements at different position have equal value,
				// that means the current element is not unique
                if (i != j && arr[i] == arr[j]) {
                    isUnique = false;
					break;
                }
            }

            if (isUnique) {
                System.out.print(arr[i] + " ");
            }
        }
		System.out.println();
        scanner.close();
    }
}

Similarly you can even print the duplicate elements.