Java TimeUnit Usage getAllCombinations( ArrayList lengths)

Description

Given a vector of sizes, every possible combination consisting of one member from each groups of a given size is returned.

License

Creative Commons License

Parameter

Parameter	Description
lengths	size of each group

Return

all combinations

Declaration

public static ArrayList<ArrayList<Integer>> getAllCombinations(
        ArrayList<Integer> lengths) 

Method Source Code

//package com.java2s;
//License from project: Creative Commons License 

import java.util.ArrayList;
import java.util.concurrent.TimeUnit;

public class Main {
    /**//from   w w w.  j a  v  a2 s .  c  o m
     * Given a vector of sizes, every possible combination consisting of one
     * member from each groups of a given size is returned. The results are
     * returned in a vector, where each member is a vector that in turn contains
     * the indices in the group of each member in that combination.
     *
     * @param lengths size of each group
     * @return all combinations
     */
    public static ArrayList<ArrayList<Integer>> getAllCombinations(
            ArrayList<Integer> lengths) {
        long start = System.currentTimeMillis();
        ArrayList<ArrayList<Integer>> combos = new ArrayList<ArrayList<Integer>>();
        getAllCombinations(lengths, 0,
                new ArrayList<Integer>(lengths.size()), combos);
        System.out.println(combos.size() + " combinations of length "
                + combos.get(0).size());
        long end = System.currentTimeMillis();
        System.out.println("Combination computation time: "
                + TimeUnit.MILLISECONDS.toMinutes(end - start)
                + " minutes (" + (end - start) + " milliseconds)");
        return combos;
    }

    /**
     * Recursive helper method for getAllCombinations above
     *
     * @param lengths sizes of all groups
     * @param idx index in lengths
     * @param soFar collection of members currently being built
     * @param combos accumulates complete combinations
     */
    public static void getAllCombinations(final ArrayList<Integer> lengths,
            int idx, ArrayList<Integer> soFar,
            ArrayList<ArrayList<Integer>> combos) {
        if (idx == lengths.size()) {
            //System.out.println(soFar);
            combos.add((ArrayList<Integer>) soFar.clone());
        } else {
            int numOptions = lengths.get(idx);
            for (int i = 0; i < numOptions; i++) {
                soFar.add(i);
                getAllCombinations(lengths, idx + 1, soFar, combos);
                soFar.remove(soFar.size() - 1);
            }
        }
    }
}

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