Stackoverflow with Quicksort Java implementation

Question

Having some problems implementing quicksort in java. I get a stackoverflow error when I run this program and I\'m not exactly sure why. If anyone can point out the error, it

Answer 1

import java.util.Arrays;


public class QuickSort {


    public static int pivot(int[] a, int lo, int hi){
        int mid = (lo+hi)/2;
        int pivot = a[lo] + a[hi] + a[mid] - Math.min(Math.min(a[lo], a[hi]), a[mid]) - Math.max(Math.max(a[lo], a[hi]), a[mid]);

        if(pivot == a[lo])
            return lo;
        else if(pivot == a[hi])
            return hi;
        return mid;
    }

    public static int partition(int[] a, int lo, int hi){

        int k = pivot(a, lo, hi);
        //System.out.println(k);
        swap(a, lo, k);
        //System.out.println(a);
        int j = hi + 1;
        int i = lo;
        while(true){

            while(a[lo] < a[--j])
                if(j==lo)   break;

            while(a[++i] < a[lo])
                if(i==hi) break;

            if(i >= j)  break;
            swap(a, i, j);
        }
        swap(a, lo, j);
        return j;
    }

    public static void sort(int[] a, int lo, int hi){
        if(hi<=lo)  return;
        int p = partition(a, lo, hi);
        sort(a, lo, p-1);
        sort(a, p+1, hi);
    }

    public static void swap(int[] a, int b, int c){
        int swap = a[b];
        a[b] = a[c];
        a[c] = swap;
    }

    public static void sort(int[] a){
        sort(a, 0, a.length - 1);
        System.out.print(Arrays.toString(a));
    }

    public static void main(String[] args) {
        int[] arr = {5,8,6,4,2,9,7,5,9,4,7,6,2,8,7,5,6};
        sort(arr);
    }
}

Try this. It will work for sure.