How to find the permutation of a sort in Java

Question

I want to sort an array and find the index of each element in the sorted order. So for instance if I run this on the array:

[3,2,4]

I\'d ge

Answer 1

Let's assume your elements are stored in an array.

final int[] arr = // elements you want
List indices = new ArrayList(arr.length);
for (int i = 0; i < arr.length; i++) {
  indices.add(i);
}
Comparator comparator = new Comparator() {
  public int compare(Integer i, Integer j) {
    return Integer.compare(arr[i], arr[j]);
  }
}
Collections.sort(indices, comparator);

Now indices contains the indices of the array, in their sorted order. You can convert that back to an int[] with a straightforward enough for loop.