gistfile1.java

private int[] a;
private int n;

public void sort(int[] a)
{
	this.a = a;
	n = a.length;
	quicksort(0, n - 1);
}

private void quicksort (int lo, int hi)
{
	int i = lo,
	    j = hi;

	int x = a[(lo + hi) / 2];

	while (i <= j) {
		while (a[i] < x) i++; 
		while (a[j] > x) j--;
		if (i <= j) {
			exchange(i, j);
			i++;
			j--;
		}
	}

	if (lo < j) quicksort(lo, j);
	if (i < hi) quicksort(i, hi);
}

private void exchange(int i, int j)
{
	int t = a[i];
	a[i] = a[j];
	a[j] = t;
}