get indexes of n smallest elements in an array

Question

I have an int array int[] myArray = new int[100]; and want to get indexes of smallest 10 (any n) elements. How can I do this?

Answer 1

If you are looking for a practical answer (versus the actual sorting alg., etc.), then just use a HashMap or PriorityQueue. If speed isn't a concern try this easy alg. It is easier than a PriorityQueue since you don't need a custom object:

HashMap> indexMap = new HashMap>();

Fill indexMap so we can get the indices for any given number in array

for (int index = 0; index <= array.size; index++) {
   if (indexMap.get(array[index]) == null) { // Prime it with an ArrayList
      indexMap.put(array[index], new ArrayList());
   }

   indexMap.get(array[index]).add(index);
}

For the smallest n numbers in array, print out their index.

Arrays.sort(array);
for (int index = 0; index <= n; index++) {
   System.out.println(indexMap.get(array[index]).remove(0));
}