Homework #1

Due: March 28 (Friday)

In homework #1, you have two programs to complete: InsertionSort.java and Utils.java.

Problem 1

Complete InsertionSort.java.

public class InsertionSort {

    /**
     * Sort an array xs in a non-increasing (i.e., decreasing) order
     * @param xs integer array
     */
    // DO NOT MODIFY THIS METHOD!!
    public static void isort(int[] xs) {
        for (int i = 1; i < xs.length; i++) {
            insert(xs, i);
        }
    }

    /**
     * Insert element xs[k] to already sorted group x[0]..x[k-1]
     * @param xs integer array
     * @param k index of element to be inserted
     */
    private static void insert(int[] xs, int k) {
        /*
            Complete code here. You must call `swap()` method.
         */
    }
}

Implementation Guidelines

• You can freely modify the body of the insert() method to complete the code. However, do not add any fields or additional methods to InsertionSort class, and no method signatures should be changed.
• You should check the correctness of your program by running test code, InsertionSortTest.java

Problem 2

Complete Utils.java. You have four methods to fill in.

public class Utils {

    /**
     * Find an index of an element matching `target`.
     * @param xs int array
     * @param target element to be found
     * @return index of a matching element, -1 otherwise
     */
    public static int findIndex(int[] xs, int target) {

        return 0;
    }

    /**
     * Calculate the sum of an array.
     * @param xs double array
     * @return sum of an array
     */
    public static double sum(double[] xs) {

        return 0.0;
    }

    /**
     * Reverse the elements of a String array. For example, ["A", "BB", "C"] => ["C", "BB", "A"]
     * @param xs String array
     * @return a newly created array containing elements of xs in reversed order
     */
    public static String[] reverse(String[] xs) {

        return null;
    }

    /**
     * Swap elements at position i and j in array xs
     * @param xs integer array
     * @param i index of element to be swapped
     * @param j index of element to be swapped
     */
    private static void swap(int[] xs, int i, int j) {
        /*
            Complete code here.
         */
    }
  
    /**
     * Reverse the elements of a String array in place without creating a new array.
     * Input array xs itself must be transformed to an array containing elements
     * in reversed order.
     * For example, ["A", "BB", "C"] => ["C", "BB", "A"].
     * @param xs String array
     */
    public static void reverse_in_place(String[] xs) {

    }

    /**
     * Returns an array containing running averages of an array.
     * @param xs int array
     * @return an array containing running average
     *
     * Given an input xs = [1, 2, 3, 4], `average()` returns a new array
     * containing running averages [1.0, 1.5, 2.0, 2.5].
     * Here,
     *      1.0 = 1 / 1
     *      1.5 = (1 + 2) / 2
     *      2.0 = (1 + 2 + 3) / 3
     *      2.5 = (1 + 2 + 3 + 4) / 4
     */
    public static double[] average(int[] xs) {

        return null;
    }

}

Implementation Guidelines

• You can freely modify the body of each method to complete the code. You can also freely add fields and private methods if necessary. However, no given public method signatures should be changed.
• You should check the correctness of your program by running test code, UtilsTest.java

What to submit?

• Your source codes archived in .zip or .jar format.
  • Subject: Homework#1, Section [A|B], 성명, 학번
  • Email to your TA (박정빈, pjb0226@hanyang.ac.kr)