Random number list without repeating Android

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Random number list without repeating Android

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#1 by (2 votes)

2

I have an ArrayList with N items inside and I need to group them randomly into 2 sets of X items and the rest into another set. However, none of them can be repeated.

For example: my ArrayList has 20 items added and I want to split it into 2 groups of 7, and the remaining 6 into another set. However, the choice of these items to compose the sets has to be random and none of those 20 can be repeated in any of the sets.

I am aware of the Random class and I am using it, but the problem is being in the moment of comparing the new numbers generated with the previous ones, so that there is no repetition.

random android lista arraylist

asked by anonymous 06.02.2016 / 03:21

1 answer

Laravel 4.2 - 405 Method Not Allowed Pass values between policies

score 2 · Accepted Answer

One possible approach is to randomly sort (shuffle) the 20-item ArrayList and extract the others.

Example for an ArrayList of 20 integers:

ArrayList<Integer> original = new ArrayList<>();
for(int i = 0; i< 20; i++){
    original.add(i);
}

//Clone o original caso o queira manter inalterado
ArrayList<Integer> embaralhado = (ArrayList<Integer>) original.clone();

//Embaralha
Collections.shuffle(embaralhado);

ArrayList<Integer> grupo1 = new ArrayList<>();
ArrayList<Integer> grupo2 = new ArrayList<>();
ArrayList<Integer> grupo3 = new ArrayList<>();

//Percorre o ArrayList embaralhado e distribui os seus itens pelos grupos.
for(int i=0; i < embaralhado.size(); i++){
   if(i < 7)grupo1.add(embaralhado.get(i));
   else if(i < 14)grupo2.add(embaralhado.get(i));
   else grupo3.add(embaralhado.get(i));
}