Lecture Notes on 26 Jul 2013

public static void allSubstrings (String s)
{
  int window = s.length();
  while (window > 0)
  {
    int start = 0;
    while ((start + window) <= s.length())
    {
      System.out.println (s.substring(start, start + window));
      start++;
    }
    window--;
  }
}

public class Permute
{
  public static void printArray (int[] a)
  {
     for (int i = 0; i < a.length; i++)
     {
       System.out.print (a[i] + " ");
     }
     System.out.println();
  }

  public static void swap (int[] a, int i, int j)
  {
    int tmp = a[i];
    a[i] = a[j];
    a[j] = tmp;
  }

  public static void permute (int[] a, int k)
  {
    if (k == a.length - 1)
    {
       printArray (a);
    }
    else
    {
      for (int i = k; i < a.length; i++)
      {
         swap (a, k, i);
	 permute (a, k + 1);
	 swap (a, i, k);
      }
    }
  }

  public static void main (String[] args)
  {
    int[] a = {1, 2, 3, 4};
    permute (a, 0);
  }
}