package fixjava;

public class StringUtils {

	/** Repeat the given string the requested number of times. */
	public static String repeat(String str, int numTimes) {
		StringBuilder buf = new StringBuilder(Math.max(0, str.length() * numTimes));
		for (int i = 0; i < numTimes; i++)
			buf.append(str);
		return buf.toString();
	}

	/**
	 * Pad the left hand side of a field with the given character. Always adds at least one pad character. If the length of str is
	 * greater than numPlaces-1, then the output string will be longer than numPlaces.
	 */
	public static String padLeft(String str, char padChar, int numPlaces) {
		int bufSize = Math.max(numPlaces, str.length() + 1);
		StringBuilder buf = new StringBuilder(Math.max(numPlaces, str.length() + 1));
		buf.append(padChar);
		for (int i = 1, mi = bufSize - str.length(); i < mi; i++)
			buf.append(padChar);
		buf.append(str);
		return buf.toString();
	}

	/**
	 * Pad the right hand side of a field with the given character. Always adds at least one pad character. If the length of str is
	 * greater than numPlaces-1, then the output string will be longer than numPlaces.
	 */
	public static String padRight(String str, char padChar, int numPlaces) {
		int bufSize = Math.max(numPlaces, str.length() + 1);
		StringBuilder buf = new StringBuilder(Math.max(numPlaces, str.length() + 1));
		buf.append(str);
		buf.append(padChar);
		while (buf.length() < bufSize)
			buf.append(padChar);
		return buf.toString();
	}

	/** Intern all strings in an array, skipping null elements. */
	public static String[] intern(String[] arr) {
		for (int i = 0; i < arr.length; i++)
			arr[i] = arr[i].intern();
		return arr;
	}

	/** Intern a string, ignoring null */
	public static String intern(String str) {
		return str == null ? null : str.intern();
	}

}

package util;

import java.math.BigInteger;

public class CombinationGenerator {

  private int[] a;
  private int n;
  private int r;
  private BigInteger numLeft;
  private BigInteger total;

  //------------
  // Constructor
  //------------

  public CombinationGenerator (int n, int r) {
    if (r > n) {
      throw new IllegalArgumentException ();
    }
    if (n < 1) {
      throw new IllegalArgumentException ();
    }
    this.n = n;
    this.r = r;
    a = new int[r];
    BigInteger nFact = getFactorial (n);
    BigInteger rFact = getFactorial (r);
    BigInteger nminusrFact = getFactorial (n - r);
    total = nFact.divide (rFact.multiply (nminusrFact));
    reset ();
  }

  //------
  // Reset
  //------

  public void reset () {
    for (int i = 0; i < a.length; i++) {
      a[i] = i;
    }
    numLeft = new BigInteger (total.toString ());
  }

  //------------------------------------------------
  // Return number of combinations not yet generated
  //------------------------------------------------

  public BigInteger getNumLeft () {
    return numLeft;
  }

  //-----------------------------
  // Are there more combinations?
  //-----------------------------

  public boolean hasMore () {
    return numLeft.compareTo (BigInteger.ZERO) == 1;
  }

  //------------------------------------
  // Return total number of combinations
  //------------------------------------

  public BigInteger getTotal () {
    return total;
  }

  //------------------
  // Compute factorial
  //------------------

  private static BigInteger getFactorial (int n) {
    BigInteger fact = BigInteger.ONE;
    for (int i = n; i > 1; i--) {
      fact = fact.multiply (new BigInteger (Integer.toString (i)));
    }
    return fact;
  }

  //--------------------------------------------------------
  // Generate next combination (algorithm from Rosen p. 286)
  //--------------------------------------------------------

  public int[] getNext () {

    if (numLeft.equals (total)) {
      numLeft = numLeft.subtract (BigInteger.ONE);
      return a;
    }

    int i = r - 1;
    while (a[i] == n - r + i) {
      i--;
    }
    a[i] = a[i] + 1;
    for (int j = i + 1; j < r; j++) {
      a[j] = a[i] + j - i;
    }

    numLeft = numLeft.subtract (BigInteger.ONE);
    return a;

  }
}
