Java ListIterator Usage toposort(Iterable<T> items, Comparator<? super T> partOrder)

Description

Brute-force topological sort, required because element types are only partially ordered: there is no ordering amongst metamodel types nor amongst unrelated specialization types.

License

Open Source License

Parameter

Parameter	Description
items	the items to be sorted
partOrder	a partial ordering relation on the items

Return

the topologically sorted items as a new mutable list

Declaration

private static <T> List<T> toposort(Iterable<T> items, Comparator<? super T> partOrder)

Method Source Code


//package com.java2s;
/*//from  www  . j a  v a 2 s .c  o m
 * Copyright (c) 2015 Christian W. Damus and others.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *    Christian W. Damus - initial API and implementation 
 */

import java.util.ArrayList;

import java.util.Comparator;

import java.util.LinkedList;
import java.util.List;
import java.util.ListIterator;

public class Main {
    /**
     * Brute-force topological sort, required because element types are only
     * partially ordered: there is no ordering amongst metamodel types nor
     * amongst unrelated specialization types. The only ordering relation is the
     * bottom-up vertex ordering in the specialization graph.
     * 
     * @param items
     *            the items to be sorted
     * @param partOrder
     *            a partial ordering relation on the items
     * @return the topologically sorted {@code items} as a new mutable list
     */
    private static <T> List<T> toposort(Iterable<T> items, Comparator<? super T> partOrder) {
        List<T> unsorted = new LinkedList<T>();
        for (T next : items) {
            unsorted.add(next);
        }

        List<T> result = new ArrayList<T>(unsorted.size());

        while (!unsorted.isEmpty()) {
            T min = unsorted.remove(0);

            for (ListIterator<T> iter = unsorted.listIterator(); iter.hasNext();) {
                T next = iter.next();
                if (partOrder.compare(next, min) < 0) {
                    // Found a new minimum. Put the old one back for next pass
                    iter.set(min);
                    min = next;
                }
            }

            // Whatever's the minimum now is the next in our partial ordering
            result.add(min);
        }

        return result;
    }
}

Java ListIterator Usage toposort(Iterable items, Comparator partOrder)