Arrays

Challenge 1:Write a program that fills an array with 10 random integers in [1, 20], asks the user to provide a value, and counts how many numbers in the array are equal to the value entered by the user. 
class lab8_1 {

    public static void main(String[] args) {
        int counter = 0;

        Scanner in = new Scanner(System.in);

        Random rand = new Random();





        int[] randomIntegers = new int[10];

        System.out.println("Provide a value: ");

        int value = in.nextInt();
        for (int i = 0; i < randomIntegers.length; i++) {
            randomIntegers[i] = 1+rand.nextInt(20);

            if (value == randomIntegers[i]) {
                counter++;
            }
            System.out.println(randomIntegers[i] + "");

        }
        System.out.println("You have " + counter + " matches");
    }

}

Challenge 2:Write a program that fills an array with 20 random integers in [1, 100] and prints the location in the array of the smallest (the minimum) integer. 
class lab8_2 {

    public static void main(String[] args) {
        int counter = 0;
        int temp;
        int loc = 0;

        Scanner in = new Scanner(System.in);

        Random rand = new Random();

        int[] randomIntegers = new int[20];

        randomIntegers[0] =1+ rand.nextInt(100);
        
        temp = randomIntegers[0];

        for (int i = 0; i < 20; i++) {





            randomIntegers[i] = 1+rand.nextInt(100);

            if (temp > randomIntegers[i]) {

                temp = randomIntegers[i];
                loc = i;
            }
            System.out.println(randomIntegers[i] + "");

        }
        System.out.println("The minimun number is: " + temp + " and is at location: " + loc);
    }

}

Challenge 3:Write a program that computes the alternating sum of all elements in an array. For example, if the array elements are

then it computes

1 4 9 16 9 7 4 9 11
1 – 4 + 9 – 16 + 9 – 7 + 4 – 9 + 11 = –2 

class lab8_3 {

    public static void main(String[] args) {
        System.out.println("Enter the elements of the array: ");
        System.out.println("Example: 1 4 9 16 9 7 4 9 11 and press ENTER");

        Scanner in = new Scanner(System.in);

        String arrayElements = in.nextLine();

        String[] nums = arrayElements.split(" ");

        int[] intArray = new int[nums.length];

        for (int i = 0; i < nums.length; i++) {
            intArray[i] = Integer.parseInt(nums[i]);
        }
        calculateSum(intArray);
    }
    public static void calculateSum(int[] array) {
        int sum = 0;
        for (int i = 0; i < array.length; i++) {
            if (i % 2 == 0) {
                sum += array[i];
                if (i != 0) {
                    System.out.print(" + " + array[i]);
                } else {
                    System.out.print(array[i]);
                }
            } else {
                sum -= array[i];
                System.out.print(" - " + array[i]);
            }
        }
        System.out.println(" = " + sum);
    }

}

Challenge 4:Write a program that determines if an array contains two adjacent duplicate elements. 

class lab8_4 {

    public static void main(String[] args) {
        int [] values ={10,20,15};
        if(checkDuplicates(values)==true){ 
        
        System.out.println("" + checkDuplicates(values));
            
        System.out.println("The array contains two adjacent duplicate elements");
        }else {
        System.out.println("The array doesnt contain two adjacent duplicate elements");
        
        }    
    }

public  static boolean checkDuplicates(int [] array){




        HashSet<Integer> hSet = new HashSet<Integer>();
        for( int i = 0; i < array.length; i++ )
        {
            if( !hSet.add(array[i]) )
               
                return true;
        }
        
        return false;
    }

}