How to get Random Number

Question

I want to get 20 random numbers between 1 to 100, but the number should not repeated....

Updated: If I have 20 names in which any 5 to be selected at random one by one but the name came once not to be called again.....

That's not random. Random sequences _do_ have repeated numbers. Can you clarify? — Oded, Nov 19 '10 at 15:37
It's not random, but it is still useful for some things (for example, randomly playing the songs on an album without any repeats). — dicroce, Nov 19 '10 at 15:38
Here you go: 4,19,50,3,10,99,7,12,71,28,17,49,83,75,44,37,96,30,15,42 — Mark Heath, Nov 19 '10 at 15:43

score 7 · Answer 1 · answered Nov 19 '10 at 15:40

Put the numbers in a list, and pick from the list:

List<int> numbers = Enumerable.Range(1, 100).ToList();

Random rnd = new Random();
List<int> picks = Enumerable.Range(1, 20).Select(n => {
  int index = rnd.Next(numbers.Count);
  int pick = numbers[index];
  numbers.RemoveAt(index);
  return pick;
});

This is probably the simplest way to solve it, but it's not the most efficient. Removing items in a list involves moving the following items. With a bit more code you could avoid that move, but for most purposes the code is good enough as it is.

score 5 · Accepted Answer · edited May 23 '17 at 11:47

5

I asked this a year or so ago.

Unique Random Numbers

The selected answer is brilliant, I thought.

edited May 23 '17 at 11:47

Community

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answered Nov 19 '10 at 15:37

dicroce

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How to get Random Number

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