functions, exercise 02, slide 35

package class170703;

import java.util.Random;

public class functions02 {
    // Functions, exercise 02, slide 35
    // input: two arrays of integer numbers
    // output: array of the common numbers (intersection)

    // building a data sample: two arrays of integers
    // then calling function intersection to calculate
    // and print results
    public static void main(String[] args) {
        // sample data for testing only
        int[] array1 = filledArray(20, 1, 50); // create and fill an array with
                                                // 20 numbers in the range 1 to
                                                // 50
        int[] array2 = filledArray(20, 1, 50); // create and fill an array
                                                // with 20 numbers in the
                                                // range 1 to 50

        // get intersection array with repeated values not allowsed
        int[] resultArrayNoRepaeat = intersection(array1, array2, false);

        // get intersection array with repeated values not allowsed
        int[] resultArrayRepaeatAllowed = intersection(array1, array2, true);

        // print to screen
        System.out.printf("first array  : %s\n", toString(array1));
        System.out.printf("second array : %s\n", toString(array2));

        System.out.printf("\nrepeated values are allowed intersection : %s \n",
                toString(resultArrayRepaeatAllowed));
        System.out.printf("\nrepeated values not allowed intersection : %s \n",
                toString(resultArrayNoRepaeat));
    }

    // create and fill an array with random integer numbers
    public static int[] filledArray(int size, int minValue, int maxValue) {
        // creating random object
        Random rnd = new Random();

        // allocate a new array
        int[] resultArray = new int[size];

        for (int i = 0; i < resultArray.length; i += 1) {
            resultArray[i] = minValue + rnd.nextInt(maxValue - minValue + 1);
        }

        return resultArray;
    }

    // find the intersection of two integer arrays
    // input: two integer arrays
    // output: an array containing the intersection the given arrays
    private static int[] intersection(int[] array1, int[] array2,
            boolean repeatAllowed) {
        // optional: to reduce function calls, array1 should be the smaller
        if (array1.length - array2.length > 10) // for example
            return intersection(array2, array1, repeatAllowed);

        // initialize an array for the result
        int[] resultArray = {};

        // for each number in array1
        for (int aNumber : array1) {
            // if it already exists in result array also
            if (isArrayContains(resultArray, aNumber)) {
                // if repeated values are allowed
                if (repeatAllowed) {
                    // add this number to the result array
                    resultArray = addToArray(resultArray, aNumber);
                }
            } else
            // if it exists in array2 also
            if (isArrayContains(array2, aNumber)) {
                // add this number to the result array
                resultArray = addToArray(resultArray, aNumber);
            }

        }

        // return the array of intersection result
        return resultArray;
    }

    // check if a number exists in an array
    // input: array of integers and an integer number
    // output: true if the number exists in the array, otherwise false
    private static boolean isArrayContains(int[] array, int aNumber) {
        // for each number in array
        for (int num : array) {
            // if it is equal to the number to be searched
            if (num == aNumber) {
                // return true
                return true;
            }
        }
        // not exist in the array, return false
        return false;
    }

    // append a number to an array
    // input: array of integers and an integer number
    // output:
    // array that contains the given array with the given number appended
    private static int[] addToArray(int[] array, int aNumber) {
        // determine the size of the given array
        int oldSize = array == null ? 0 : array.length;

        // define a new array with one more cell than the given array
        int[] newArray = new int[oldSize + 1];

        // copy the numbers from the given array to the new one
        for (int i = 0; i < oldSize; i += 1) {
            newArray[i] = array[i];
        }

        // add the given number to empty cell at the end of the new array
        newArray[oldSize] = aNumber;

        // return the new array
        return newArray;
    }

    // convert an array of integer numbers to a string
    // input: an array of integer values
    // output: a string with all values from the array separated by comma
    public static String toString(int[] array) {
        // if array is empty
        if (array.length == 0) {
            // return result and quit
            return "[]";
        }

        // building a string from all numbers in the array
        String result = "" + array[0]; // start with the first number

        // scan the numbers in the array without the first
        for (int i = 1; i < array.length; i += 1) {
            // convert number to string and add it to the result string
            result += ", " + array[i];
        }

        // return the result surrounded by brackets
        return "[" + result + "]";
    }
}