I need to generate an random array from a bigger array of int without repetition and in a range of numbers.
For e.g I have an array a[] with 1-200 int , What i need is random number array from all 200 int but of size 15.How could I implement this?
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2 Answers
Fisher-Yates shuffle. In particular, shuffle just the first 15 elements and select them.
5 Comments
bezmax
In particular, shuffle just the first 15 elements and select them. - sorry, but I didn't really get this part. Can you elaborate please?
Peter Lawrey
+1 The shuffle selects a random element for each cell in turn. Since you only need 15 you can stop once you have done the 15th cell.
aioobe
There should be no dupes though.
Joey
aioobe, their initial array contains no duplicates as far as I understood the question.
Joey
Note: Unless modifying the algorithm to work on new arrays (usually it's in-situ), this will modify the initial array of numbers which may or may not be a problem.
Random rnd = new Random();
int[] a = new int[200];
for (int i = 0; i < a.length; i++)
a[i] = i;
int[] r = new int[15];
for (int i = 0; i < r.length; i++) {
int j = rnd.nextInt(a.length - i);
r[i] = a[j];
a[j] = a[a.length - i - 1];
}
That should do it. Random grab something from a. Once you've grabbed it, replace it with the "last" value of a. The "last" value is easily derived from a.length and i.
1 Comment
Hounshell
No prob. Remember, this modifies a.