Answer:
The Java code is given below with appropriate comments in key areas of the code
Explanation:
import java.util.TreeMap;
public class HW1 {
/**
* Inverts an array of Strings by returning a TreeMap that maps Strings to the
* smallest index in the array that contains the String.
*
* @param a an array of Strings
* @return a Map that given a String returns the smallest index of the array
* that contains the String (or null if String is not in the array a).
*/
public static TreeMap<String, Integer> invert(String[] a) {
TreeMap<String, Integer> tmap = new TreeMap<>();
for (int i = 0; i < a.length; i++) {
if (!tmap.containsKey(a[i])) {
tmap.put(a[i], i);
}
}
return tmap;
}
/**
* Computes the total number of occurrences of every String in an array.
*
* @param a an array of Strings
* @return a Map that given a String returns the number of occurrences of that
* String in the array (or null if String is not in the array a).
*/
public static TreeMap<String, Integer> count(String[] a) {
TreeMap<String, Integer> tmap = new TreeMap<>();
for (int i = 0; i < a.length; i++) {
tmap.put(a[i], 1 + tmap.getOrDefault(a[i], 0));
}
return tmap;
}
}
