In java Most simple way to add non duplicate random numbers to 2D Array

Question

I'm trying to figure out whats the most simple way to add to fill this 2D Array with only non duplicate numbers.

I've tried to use a method with boolean to check the value before adding it, if it already exists but I couldn't make it work.

int[][] x = new int[R][C];

for (int i = 0; i < x.length; i++) {
    for (int j = 0; j < x[i].length; j++) {
        double z = (Math.random() * ((30 * (j + 1)) - ((30 * j) + 1)) + 1 + ((30 * j) + 1));
        card[i][j] = (int) z;
    }
}

please read [mcve] and edit your post accordingly. – Dev Nov 09 '19 at 13:33 — Dev, Nov 09 '19 at 13:33

Karol Dowbecki · Answer 1 · 2019-11-09T17:09:33.917

0

You definitely want to use Random.nextInt() to get a uniform distribution of your int. Most likely you want a Set to track which numbers were already generated.

int[][] cards = new int[ROW][COL];
Random r = new Random();
Set<Integer> generated = new HashSet<>();
for (int i = 0; i < ROW; i++) {
  for (int j = 0; j < COL; j++) {
    int n;
    do {
      n = r.nextInt();
    } while (generated.contains(n));
    generated.add(n);
    cards[i][j] = n;
  }
}

edited Nov 09 '19 at 17:09

answered Nov 09 '19 at 13:32

Karol Dowbecki

43,645
9
78
111

Then it's not random anymore. The question was specifically about using Random numbers. – Ramu Nov 09 '19 at 14:49

score 0 · Answer 2 · answered Nov 09 '19 at 13:37

The best way i will say is to use Set data structure

int row = 2;
int col = 2;
Set<Set<Integer>> rowSet = new HashSet<>();

 for (int i = 0; rowSet.size() < row; i++) {
        Set<Integer> colSet = new HashSet<>(); 

    for (int j = 0; colSet.size() < col; j++) {
    double x = (Math.random() * ((15 * (j + 1)) - ((15 * j) + 1)) + 1 + ((15 * j) + 1));
    colSet.add((int) x);
  }
   rowSet.add(colSet);
}

And finally convert them to array

int[][] arr = set.stream()
                     .map(i->i.stream()
                             .mapToInt(Integer::intValue)
                             .toArray())
                     .toArray(int[][]::new);

In java Most simple way to add non duplicate random numbers to 2D Array

2 Answers2