/**
 * Finds the minimum od A[lo:hi], swaps it with A[lo], recur on A[lo+1:hi].
 *
 * Correponds to splitting the array at the low index after putting
 * the minimum element there, sort the two parts, and join the sorted
 * part.  The join is trivial.  It's the splitting that requires some
 * work.  As such this selection sort belongs to the same family as
 * quick sort. 
 *
 * @author Dung X. Nguyen - Copyright 1999 - all rights reserved.
 * @since 11/28/99
 */
public class SelectionSorter extends ASorter
{
  public final static SelectionSorter Singleton = new SelectionSorter ();

  private SelectionSorter()
  {
  }

  /**
   * Finds the minimum of A[lo:hi] and swaps it with A[lo].
   * @param A 
   * @param lo 
   * @param hi 
   * @return lo + 1, and A[lo] is the minimum of A[lo:hi].
   */
  public int split(int[] A, int lo, int hi)
  {
    int s = lo;
    int i = lo + 1;

    // Invariant: A[s] <= A[lo:i-1].
    // Scan A to find minimum:
    while (i <= hi)
      {
	if (A[i] < A[s])
	  s = i;
	i++; // Invariant is maintained.
      } // On loop exit: i = hi + 1; also invariant still holds;
        // this makes A[s] the minimum of A[lo:hi].

    // Swapping A[lo] with A[s]:
    int temp = A[lo];
    A[lo] = A[s];
    A[s] = temp;
    return lo + 1;

    /*
     * Exercise for the student: write an equivalent for loop.
     */
  }

  /**
   * @param A  A[lo] is the minimum of A[lo:hi], and A[lo+1:hi] is sorted.
   * @param lo
   * @param s  == lo + 1.
   * @param hi 
   */
  public void join(int[] A, int lo, int s, int hi)
  {
    // There is nothing to do here!
  }

  public static void main(String[] args)
  {
    int[] A = {99, -34, 0, 5, -7, 0};
    System.out.println("A =");
    for (int i = 0; i < A.length; i++)
      {
	System.out.print(A[i] + "  ");
      }
    System.out.println();
    System.out.println("Sorting A...");
    SelectionSorter.Singleton.sort(A, 0, A.length - 1);
    System.out.println("Sorted A =");
    for (int i = 0; i < A.length; i++)
      {
	System.out.print (A[i] + "  ");
      }
    System.out.println("\nDone");
  }
}