flutter how to generate random numbers without duplication

Question

Is there any way to generate random numbers without duplication? For instance I want to generate 50 random numbers from 1 to 100 no duplication, any way to do this or do I have to check every time incoming number is already created or not?

If it's only small range of integer you can use hash table to keep all free number. Then pop it out at random index. — kitta
– kitta, Commented Sep 30, 2018 at 10:13
you can create an array of integer with 1 to 100 number and shuffle it using shuffle method and used as much as number you require. — Viren V Varasadiya
– Viren V Varasadiya, Commented Sep 30, 2018 at 10:40
shuffle sounds good to me. Is it not generating same number? — Daibaku
– Daibaku, Commented Sep 30, 2018 at 11:04

Viren V Varasadiya · Accepted Answer · 2018-09-30 11:29:25Z

7

you can use shuffle as following code.

import 'dart:math';

var list = new List<int>.generate(10, (int index) => index); // [0, 1, 4]
list.shuffle();
print(list);

answered Sep 30, 2018 at 11:29

Viren V Varasadiya

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2 Comments

Daibaku Over a year ago

Thank you for the example. Can I get first 5 shuffled numbers?

Viren V Varasadiya Over a year ago

you can get using list.sublist(0,5).

GeoGlass · Accepted Answer · 2020-07-07 12:26:52Z

0

You can use Set. Each object can occur only once when using it. Just try this:

Set<int> setOfInts = Set();
while (setOfInts.length < 50) {
  setOfInts.add(Random().nextInt(range) + 1);
}

You can read the documentation here: Set Doc

answered Jul 7, 2020 at 12:26

GeoGlass

1

Comments

Dr G · Accepted Answer · 2022-02-13 21:25:20Z

Here is an alternative that avoids creating an array of all the possible values, and avoids repeatedly looping until no collision occurs. It may be useful when there is a large range to select from.

import 'dart:math';

class RandomList {
  static final _random = new Random();

  static List<int> uniqueSample({int limit, int n}) {
    final List<int> sortedResult = [];
    final List<int> result = [];
    for (int i = 0; i < n; i++) {
      int rn = _random.nextInt(limit - i); // We select from a smaller list of available numbers each time

      // Increment the number so that it picks from the remaining list of available numbers
      int j = 0;
      for (; j < sortedResult.length && sortedResult[j] <= rn; j++) rn++;

      sortedResult.insert(j, rn);
      result.add(rn);
    }
    return result;
  }
}

I haven't tested it exhaustively but it seems to work.

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