I am encountering a problem generating 6 random numbers between 1 and 6 in Java. All the numbers have to be unique. When I enter kolon value 5, the arrays should be like this:
1 2 3 4 5 6
1 2 3 4 5 6
1 2 3 4 5 6
1 2 3 4 5 6
I don't want the program to generate the same two numbers. What is wrong here?
Relevant code:
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
System.out.println("Please enter row quantity: ");
int kolon = input.nextInt();
Integer[][] dizi_asil = new Integer[kolon][6];
for (int i = 0; i < kolon; i++) {
Integer[] dizi = new Integer[6];
for (int j = 0; j < 6; j++) {
dizi[j] = (int) ((Math.random() * 6) + 1);
for (int u = 0; u < 1; u++) {
for (int k = 0; k < j; k++) {
while (dizi[k] == dizi[j]) {
dizi[j] = (int) ((Math.random()* 6) + 1);
u++;
}
}
}
dizi_asil[i][j] = dizi[j];
}
Arrays.sort(dizi_asil[i]);
}
for (int i = 0; i < dizi_asil.length; i++) {
for (int k = 0; k < dizi_asil[i].length; k++) {
System.out.print(dizi_asil[i][k] + "\t");
}
System.out.println();
}
create a list containing 1 to 6. then shuffle it using Collection.shuffle . Then you will get random unique number
This is an easy way:
List<Integer> list = Arrays.asList(1,2,3,4,5,6);
Collections.shuffle(list);
// you can convert it to an array if you need to.
A very simple fix - replace u++;
with u--;
. ++
will make the loop stop, --
will make it carry on.
Though I'd suggest something more like the below. I hope it's easy enough to understand.
Integer[] dizi = new Integer[6];
for (int j = 0; j < 6; j++)
{
boolean isValid;
do
{
dizi[j] = (int) ((Math.random() * 6) + 1);
isValid = true;
for (int k = 0; isValid && k < j; k++)
if (dizi[k] == dizi[j])
isValid = false;
}
while (!isValid);
dizi_asil[i][j] = dizi[j];
}
I'd also suggest the Random class , which has a nextInt(int)
method, which is better than (int) ((Math.random() * 6) + 1)
.
But shuffling is probably a faster way to do it. Either use the API like one of the other answers or look into the Fisher-Yates / Knuth shuffle for an easy shuffle algorithm.
Try Collections.shuffle(list);
List<Integer> list = new ArrayList<Integer>();
for(int i = 1; i<7 ; i++)
list.add(i);
Or you can do :
List<Integer> list = Arrays.asList(1,2,3,4,5,6)
Collections.shuffle(list);
Iterate the list and get unique value each time.
A much shorter way is to use shuffle as many have mentioned already.
public static void main(String... ignored) {
Scanner input = new Scanner(System.in);
System.out.println("Please enter row quantity: ");
List<Integer> rolls = Arrays.asList(1, 2, 3, 4, 5, 6);
for (int i = 0, rows = input.nextInt(); i < rows; i++) {
Collections.shuffle(rolls);
System.out.println(rolls);
}
}
if you run it you get something like
Please enter row quantity:
5
[5, 6, 3, 2, 4, 1]
[5, 4, 3, 6, 2, 1]
[6, 4, 2, 3, 5, 1]
[3, 1, 6, 2, 5, 4]
[4, 1, 6, 3, 5, 2]
Imports:
import acm.util.RandomGenerator;
private RandomGenerator rgen = RandomGenerator.getInstance();
Actually picking:
randnum = rgen.nextInt(1, 6);
This picks a random number between 0 and 5. You can just do this for 1 through 6:
randnum = rgen.nextInt(2, 7);
Or:
randnum = rgen.nextInt(1, 6);
randnum++;
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