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The following method definition is provided in the program:
ArrayList<Integer> lotterynumbers(Random r)
Write an implementation of the method that returns the lottery numbers in the list.
There are seven numbers, ranging from [1, 39].
The same number cannot appear twice in the list.
Example method call:
public static void main(String[] args){
Random rnd = new Random();
System.out.println(lotterynumbers(r));
System.out.println(lotterynumbers(r));
}
Example output:
[37, 14, 32, 20, 28, 21, 25]
[20, 6, 23, 30, 13, 11, 26]
==================================
import java.util.Random;
import java.util.ArrayList;
import java.util.HashSet;
public class Test{
public static void main(String[] args){
final Random r = new Random();
System.out.println("Testing...");
ArrayList<Integer> nrot1 = lotterynumbers(r);
ArrayList<Integer> nrot2 = lotterynumbers(r);
System.out.println("Numbers: " + nrot1);
System.out.println("");
// check 7 numbers
System.out.print("Seven numbers in the list: ");
System.out.println(nrot1.size() == 7 ? "Ok" : "No");
// check 1-39
boolean limit = true;
for (int nro : nrot1) {
if (nro < 1 || nro > 39) limit = false;
}
System.out.print("Numbers between 1 and 39: ");
System.out.println(limit ? "Ok" : "No");
// check unique
HashSet<Integer> hs = new HashSet<>(nrot1);
boolean same = hs.size() == 7;
System.out.print("All numbers unique: ");
System.out.println(same ? "Ok" : "No");
// check both lists are different in content
boolean diff = !(nrot1.equals(nrot2));
System.out.print("Random numbers: ");
System.out.println(diff ? "Ok" : "No");
}
// RETURN a list of 7 integers
public static ArrayList<Integer> lotterynumbers(Random r) {
ArrayList<Integer> numbers = new ArrayList<>();
for (int i=0; i<7; i++) {
// r.nextInt(39) => generates 0 to 38
// +1 => adjusts the range to '1 to 39'
int nro = r.nextInt(39) + 1;
// check if number is unique - then add to the list
if (!numbers.contains(nro)) {
numbers.add(nro);
}
else {
// adjust idx 'i' back by 1 to generate a new number through the loop
i--;
}
}
return numbers;
}
}
Testing...
Numbers: [31, 4, 8, 3, 17, 32, 1]
Seven numbers in the list: Ok
Numbers between 1 and 39: Ok
All numbers unique: Ok
Random numbers: Ok
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