Calculates the power set of the given collection. - Java java.util

Java examples for java.util:Collection Algorithm

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Description

Calculates the power set of the given collection.

Demo Code


//package com.java2s;
import java.util.ArrayList;
import java.util.Collection;
import java.util.List;

public class Main {
    public static void main(String[] argv) throws Exception {
        Collection list = java.util.Arrays.asList("asdf", "java2s.com");
        System.out.println(powerset(list));
    }//  ww  w . j  av  a  2 s  . com

    /**
     * Calculates the powerset of the given collection.
     * Taken from: http://rosettacode.org/wiki/Power_Set#Java
     * @param list
     * @return
     */
    public static <T> List<List<T>> powerset(Collection<T> list) {
        List<List<T>> powerset = new ArrayList<List<T>>();
        ArrayList<T> emptySet = new ArrayList<T>();
        powerset.add(emptySet); // add the empty set

        // for every item in the original list
        for (T item : list) {
            List<List<T>> newPs = new ArrayList<List<T>>();

            for (List<T> subset : powerset) {
                // copy all of the current powerset's subsets
                newPs.add(subset);

                // plus the subsets appended with the current item
                List<T> newSubset = new ArrayList<T>(subset);
                newSubset.add(item);
                newPs.add(newSubset);
            }

            // powerset is now powerset of list.subList(0, list.indexOf(item)+1)
            powerset = newPs;
        }

        //Remove the empty set
        powerset.remove(emptySet);
        return powerset;
    }
}

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