Recursive selection sort stack overflow

Question

hi, first time posting here.
i have to write a java method that implements a selection sort. This method must be recursive. ok not a problem. i have come up with this so far
    public int findMin(int index) {
        int min = index - 1;
        if (index < num.length - 1) min = findMin(index + 1);
        if (num[index] < num[min]) min = index;
        return min;
    public void selectionSort(int left) {
        if (left < num.length - 1) {
            swap(left, findMin(left));
            selectionSort(left + 1);
    public void swap(int index1, int index2) {
        int temp = num[index1];
        num[index1] = num[index2];
        num[index2] = temp;
    }which works fine until i toss in a lot of values into the array. this creates a stack overflow, and ive been told that i need to use the divide and conquer method of resolving this issue. I guess this means to split the array up and sort each half seperatly, again and agin, or so im told.
My question is how do i go about doing this, i am at a loss. Any help at all would be great.
thank you
lance

Answer 1

i get this when i push the array passed about 5500 in sizeI got no problem. Post a small demo code that is generally compilable, runnable and could reproduce your problem. See: http://homepage1.nifty.com/algafield/sscce.html and http://www.yoda.arachsys.com/java/newsgroups.html
It is silly to implement selection sort with recursion, double-silly if you use double-recursion as your current code.
/* silly but no OOME when used against 5500 element array */
import java.util.*;
public class RecursiveSelectionSort{
  static int[] num;
  public static int findMin(int index) {
    int min = index; // your code had a bug here
    if (index < num.length - 1){
      min = findMin(index + 1);
    if (num[index] < num[min]){
      min = index;
    return min;
  public static void selectionSort(int left) {
    if (left < num.length - 1) {
      swap(left, findMin(left));
      selectionSort(left + 1);
  public static void swap(int index1, int index2) {
    int temp = num[index1];
    num[index1] = num[index2];
    num[index2] = temp;
  public static void main(String[] args){
    Random rand = new Random();
    int n = 10;
    if (args.length > 0){
      n = Integer.parseInt(args[0]);
    num = new int[n];
    for (int i = 0; i < num.length; ++i){
      num[i] = rand.nextInt(10000);
    selectionSort(0);
    for (int in : num){
      System.out.print(in + " ");
    System.out.println();
}