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 Newbie Member 18Oct2010,16:45 This is the code: Code: ```//-------------------------------------- // Systematically generate combinations. //-------------------------------------- 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; } }``` Last edited by shabbir; 18Oct2010 at 17:41.. Reason: Code blocks