r.nextInt(39)

Week 3: Objects, files and exceptions/13b. Draw lottery numbers

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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
+