QuickSort

quicksort.java

public class QuickSort
{
  private int[] a;
  private int n;
  
  public void sort(int[] b)
  {
    this.a=b;
    n=a.length;
    qs(0, n-1);
  }

  private void qs(int lo, int hi)
  {
    if (lo>=hi)
      return;
    int x=a[lo+hi/2];
    int i=lo, j=hi;
    while (i<=j)
    {
      while (a[i]<x) i++;
        while (a[j]>x) j--;
          if (i<=j)
            swap(i++, j--);
    }
    qs(lo, j);
    qs(i, hi);
  }

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