MapExperts.java

package part02;

import java.util.List;
import java.util.Map;

/**
 * This class contains a set of methods that you need to implement.
 *
 * Do not change the method signatures or fields, as these will be used by the
 * automated tests.
 *
 * These exercises have been applied from the course material of the MOOC
 * programming course (https://ohjelmointi-23.mooc.fi/osa-5). CC BY-NC-SA 4.0
 */
public class MapExperts {

    /**
     * Returns a Map containing the letters of the given word as keys and the
     * number of occurrences of each letter as values.
     *
     * For example, if the word is "hello", the returned Map contains the
     * following key-value pairs: { h -> 1, e -> 1, l -> 2, o -> 1 }
     *
     * You can assume that all letters are in lower case and that the given word
     * contains only letters.
     */
    public Map<Character, Integer> countLetters(String word) {
        /*
         * Hint: you can get the characters of a String using either the charAt() method
         * or the toCharArray() method. charAt() returns a single character and
         * toCharArray() returns an array of characters.
         */
        return null;
    }

    /**
     * Returns a new map that has the keys and values of the given map swapped.
     *
     * For example, if the given map contains the key-value pairs
     * { "one" -> 1, "two" -> 2, "three" -> 3 }
     * then the returned map contains the key-value pairs
     * { 1 -> "one", 2 -> "two", 3 -> "three" }
     */
    public Map<Integer, String> reverseMap(Map<String, Integer> map) {
        /*
         * The keys of a map are always unique, so we can't have two keys with the same
         * value. However, there is no such restriction for the values of a map:
         *
         * { "apples" -> 1, "oranges" -> 1 }
         *
         * If the given map contains multiple keys with the same value, as above, you
         * can choose any of the keys to be the value of the reversed map. So either
         * { 1 -> "apples" } or { 1 -> "oranges" } will be accepted.
         */
        return null;
    }

    /**
     * Creates a new map from the given list of Course objects. The keys of the map
     * are the course codes and the values are the Course objects. You can assume
     * that the course codes are unique.
     *
     * For example, if the list contains the following Course objects:
     * [Course("SOF001AS3A", "Ohjelmointi 2"),
     * Course("SOF004AS2A", "Python-ohjelmointi")]
     *
     * Then the returned map contains the following key-value pairs:
     *
     * "SOF001AS3A" -> Course("SOF001AS3A", "Ohjelmointi 2")
     * "SOF004AS2A" -> Course("SOF004AS2A", "Python-ohjelmointi")
     */
    public Map<String, Course> createMapFromList(List<Course> list) {
        /*
         * Each Course object has a code and a name. You can access them using the
         * code() and name() methods:
         *
         * String code = course.code();
         * String name = course.name(); // you won't need this in the exercise
         */
        return null;
    }
}