Main.java

//TIP To <b>Run</b> code, press <shortcut actionId="Run"/> or
// click the <icon src="AllIcons.Actions.Execute"/> icon in the gutter.

import javax.swing.*;
import java.util.Arrays;
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        //TIP Press <shortcut actionId="ShowIntentionActions"/> with your caret at the highlighted text
        // to see how IntelliJ IDEA suggests fixing it.


        int[] arrA = {1, 2, 3, 4, 5};
        int num = arrA.length;
        int sumA = 0;
        int maxA = arrA[0];
        int[] arrB = new int[num];
        int[] arrC = new int[num];


        // 1. copying array A in array B and inverse order copying array A in array C
        for (int i = 0; i < arrA.length; i++) {
            arrB[i] = arrA[i];
            arrC[arrA.length - 1 - i] = arrA[i];
        }
        System.out.println("Homework(B) - #1");
        System.out.println(Arrays.toString(arrA));
        System.out.println("\nHomework(B) - #1.1");
        System.out.println(Arrays.toString(arrB));
        System.out.println("\nHomework(B) - #1.2");
        System.out.println(Arrays.toString(arrC));
        System.out.println("\n------------------------------------------");


        // 2 & 3. Sum of the array A elements using for-each and the max element of array A
        for (int a : arrA) {
            if (a >= maxA) {
                maxA = a;
            }
            sumA += a;
        }
        System.out.println("Homework(B) - #2");
        System.out.println(sumA);
        System.out.println("\n------------------------------------------");

        System.out.println("Homework(B) - #3");
        System.out.println(maxA);
        System.out.println("\n------------------------------------------");

        // 4. Printing odd and even elements separately.
        System.out.println("\nHomework(B) - #4");

        System.out.println("Even numbers: ");
        for (int b : arrA) {
            if (b % 2 == 0)
                System.out.println(b);
        }

        System.out.println("Odd numbers: ");
        for (int b : arrA) {
            if (b % 2 != 0)
                System.out.println(b);
        }

        System.out.println("The sum of array A is " + sumA + " and the max element is " + maxA);
        System.out.println("\n------------------------------------------");

        System.out.println("\nHomework(B) - #5");
        // 5. Showing only even index in one array. I did not understand completely the question.
        char[] arrD = {'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i'};
        for (int i = 0; i < arrD.length; i++) {
            if (i % 2 == 0)
                System.out.print(arrD[i] + ", ");
        }
        System.out.println("\n------------------------------------------");


        // 6. Sorting. Q1: Arrays.sort() method sort the array from small to great?
        System.out.println("\nHomework(B) - #6");
        // Q2: Why this line does not work? int[] arrG = Arrays.sort(arrF); The error says that it returns void.
        // Q3: What if I want to create the descending array in a new array. Array.clone()?
        int[] arrF = {1, 2, 3, 2, 5, 1, 4, 2, 5};
//        Arrays.sort(arrF);
//        int[] arrG = arrF;

        for (int i = 0; i < arrF.length - 1; i++) {
            for (int j = 0; j < arrF.length - 1 - i; j++) { //1
                if (arrF[j] < arrF[j + 1]) {
                    int temp = arrF[j];
                    arrF[j] = arrF[j + 1];
                    arrF[j + 1] = temp;
                }
            }
        }

        System.out.print(Arrays.toString(arrF));
        System.out.println("\n------------------------------------------");


        //7. Deleting repetitive elements in an array
        System.out.println("\nHomework(B) - #7");

        int[] arrH = {1, 2, 3, 2, 5, 1, 4, 2, 5}; // [1, 1, 2, 2, 2, 3, 4, 5, 5]
        Arrays.sort(arrH);

        int N = 1; // I fix it to one because the code below counts the number of transitions though miss one group of numbers
        for (int i = 1; i < arrH.length; i++) {
            //for (int j = 0; j < i; j++){
            if (arrH[i] != arrH[i - 1])
                N++; //5
        }
        //}


        int[] arrHRefined = new int[N];
        arrHRefined[0] = arrH[0]; // I need to fix the first element if not as I start i from 0 I will miss the first element. If I start
        int index = 1;
        // i from 0 my loop goes to one element more than array length
        for (int i = 1; i < arrH.length; i++) {
            if (arrH[i] != arrH[i - 1]) {
                arrHRefined[index++] = arrH[i];
            }
        }


        System.out.println(Arrays.toString(arrH));
        System.out.println(Arrays.toString(arrHRefined));
        System.out.print(N);
        System.out.println("\n------------------------------------------");

        //8. Not resolved
        System.out.println("\nHomework(B) - #8");

        int[] defArr = {1, 2, 3, 2, 5, 1, 4, 2, 5};
        // defArr = {1, 2, 3,-1, 5,-1, 4,-1,-1};
        //    fr = {2, 3, 1, 0, 2, 0, 1, 0, 0};
        // newArr= {0, 0, 0}

        int count;
        int n = 0;
        int[] fr = new int[defArr.length]; // {0, 0, 0, 0, 0, 0, 0, 0, 0};

        for (int i = 0; i < defArr.length - 1; i++) {
            if (defArr[i] == -1)
                continue;

            count = 1;

            for (int j = i + 1; j < defArr.length; j++) {
                if (defArr[i] == defArr[j]) {
                    defArr[j] = -1; // refine repetitive item
                    count++; // count how many times each item repeated
                }
            }

            fr[i] = count;
            if (count > 1)
                n++;
        }

        int[] newArr = new int[n]; // newArr= {0, 0, 0}
        int indx = 0;
        for (int k = 0; k < defArr.length; k++) {
            if (fr[k] > 1) {
                newArr[indx] = defArr[k];
                System.out.println("frequency of " + newArr[indx++] + " is: " + fr[k]);
            }

        }

        System.out.println(Arrays.toString(newArr));


        System.out.println("\n------------------------------------------");
        System.out.println("\nHomework(A) - #5");

        Scanner scanner = new Scanner(System.in);
        double a, b, c, max;

        System.out.println("1st digit");
        a = scanner.nextDouble();
        System.out.println("2nd digit");
        b = scanner.nextDouble();
        System.out.println("3rd digit");
        c = scanner.nextDouble();

//        max = a;
//        if (b> max)
//            max = b;
//        if (c > max)
//            max = c;


//        max = a;
//        max = b> max ? b : max;
        max = a > b ? a : b;
        max = c > max ? c : max;

        System.out.println("max is : " + max);


    }


}