de.invation.code.toval.math.CombinationsCalculator Maven / Gradle / Ivy

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TOVAL comprises a set of java classes for common programming issues. It includes utils for arrays, lists, sets and collections for convenient handling and modification, but also support for mathematic definitions concerning logic (clauses + resolution) together with some algorithms for permutations, powersets and resolution. Additionally it contains a number of types for multisets, matrices with object keys and much more.

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package de.invation.code.toval.math;

import java.util.Iterator;
import java.util.List;
import java.util.NoSuchElementException;

import de.invation.code.toval.misc.ArrayUtils;
import de.invation.code.toval.validate.Validate;

public class CombinationsCalculator implements Iterator{
	
	private Object[] originalArray = null;
	private int combinationLength = 0;
	private long numCombinations = 0;
	private long calculatedCombinations = 0;
	
	private int[] lastIndexCombination = null;
	
	@SuppressWarnings("unchecked")
	public CombinationsCalculator(List originalList, int combinationLength){
		this((T[]) originalList.toArray(), combinationLength);
	}
	
	public CombinationsCalculator(T[] originalArray, int combinationLength){
		Validate.notNull(originalArray);
		Validate.bigger(originalArray.length, 0);
		Validate.bigger(combinationLength, 0);
		Validate.isTrue(combinationLength <= originalArray.length);
		
		this.originalArray = originalArray;
		this.combinationLength = combinationLength;
		numCombinations = MathUtils.binCoeff(originalArray.length, combinationLength);
		lastIndexCombination = ArrayUtils.createAndInitializeArray(combinationLength, 0);
	}

	@Override
	public boolean hasNext() {
		return calculatedCombinations < numCombinations;
	}

	@SuppressWarnings("unchecked")
	@Override
	public T[] next() {
		if (!hasNext()) {
            throw new NoSuchElementException();
        }
		
        Object[] result = new Object[combinationLength];
        for (int i = 0; i < combinationLength; i++) {
            result[i] = originalArray[lastIndexCombination[i]];
        }

        for (int i = combinationLength - 1; i >= 0; i--) {
            if (lastIndexCombination[i] < originalArray.length - combinationLength + i) {
                lastIndexCombination[i]++;
                for (int j = i + 1; j < combinationLength; j++) {
                    lastIndexCombination[j] = lastIndexCombination[i] - i + j;
                }
                break;
            }
        }
        
        calculatedCombinations++;
        return (T[]) result;
	}

	@Override
	public void remove() {}

//	public static void main(String[] args) {
//		List arr = ListUtils.createAndInitializeList(100, new Integer(1));
//		System.out.println(arr);
//		CombinationsCalculator calc = new CombinationsCalculator(arr, 2);
//		long start = System.currentTimeMillis();
//		while(calc.hasNext()){
//			calc.next();
//		}
//		TimeValue time = new TimeValue(System.currentTimeMillis() - start, TimeScale.MILLISECONDS);
//		time.adjustScale();
//		System.out.println(time);
//	}

}