Question:
I have the following question, I have an array
of integers with n elements, what I need is for the element and the number of times it is repeated to be returned in a twodimensional array
, here is an example:
 n = 9

array
= {1, 2, 2, 1, 1, 3, 5, 1, 2}  The result would be: arrayTwodimensional = { {1,4}, {2,3}, {3,1}, {5,1} }
I have the following code:
int contador = 0;
int[] ar = {1, 2, 2, 1, 1, 3, 5, 1, 2};
for (int i = 0; i < ar.length; i++) {
for (int j = 0 ; j < ar.length; j++)
if(ar[i] == ar[j])
contador++;
System.out.print(contador + ",");
contador = 0;
}
And as a result I get the following:
4,3,3,4,4,1,1,4,3,
Which are the times that each element is repeated, only that in the previous code they are repeated. At this point I really don't know how to proceed.
Note: I know that with an ArrayList it could be solved much better, but for this time I would like it to be only with arrays.
Please, I hope you can help me with this concern.
Answer:
The best way is to use a Set
, this does not allow duplicate elements
List aLista = Arrays.asList(ar);
Set<Integer> miSet = new HashSet<Integer>(aLista);
for(int s: miSet){
System.out.println(s + " " +Collections.frequency(aLista,s));
}
You can read about Collections.frequency() , it returns an integer
And you can read about Set , which does not allow to enter two equal values
More formally, a set does not contain a pair of elements e1 and e2 such that e1.equals(e2)