I have an array of numbers, let's say for example it's
[1, 3, 5, 7, 9] It is possible to generate 5! that is 120 unique sequences of these numbers. For example
1 3 5 7 9 5 1 3 9 7 7 3 9 5 1 1 7 9 5 3 ... and so forth I need to generate 10 of these sequences randomly, with no duplicates. Any suggestions would be much appreciated.
List<Integer> template = Arrays.asList(1, 3, 5, 7, 9); Set<List<Integer>> seen = new HashSet<List<Integer>>(); for (int i = 0; i < 10; ++i) { List<Integer> items = new ArrayList<Integer>(template); do { Collections.shuffle(items); } while (!seen.add(items)); System.out.println(items); } :-)
What you want is to generate n random permutations of a given array. There is a simple algorithm for generating one random permutation, which is well explained on wikipedia. You still have to check for uniqueness, though.
In Java :
Random rand = new Random(); int[] generateRandomPermutation(int n) { int[] res = new int[n]; for (int i = 0; i < n; i++) { int d = rand.nextInt(i+1); res[i] = res[d]; res[d] = i; } return res; } Another solution is to use a permutation numbering scheme (presented here), and generate the corresponding permutation of n random distinct integers (from 0 to s!-1, where s is the size of the array).
