edu.wpi.checksims.util.PairGenerator.java Source code

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Here is the source code for edu.wpi.checksims.util.PairGenerator.java

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/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License (the "License").
 * You may not use this file except in compliance with the License.
 *
 * See LICENSE.txt included in this distribution for the specific
 * language governing permissions and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at LICENSE.txt.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information: Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 *
 * Copyright (c) 2014-2015 Matthew Heon and Dolan Murvihill
 */

package edu.wpi.checksims.util;

import edu.wpi.checksims.submission.Submission;
import org.apache.commons.lang3.tuple.Pair;

import java.util.*;

import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;

/**
 * Generates unordered pairs of submissions.
 */
public final class PairGenerator {
    private PairGenerator() {
    }

    /**
     * Generate all possible unique, unordered pairs of submissions.
     *
     * @param submissions Submissions to generate pairs from
     * @return Set of all unique, unordered pairs of submissions
     */
    public static Set<Pair<Submission, Submission>> generatePairs(Set<Submission> submissions) {
        checkNotNull(submissions);
        checkArgument(submissions.size() >= 2, "Cannot generate pairs with less than 2 submissions!");

        Set<Pair<Submission, Submission>> pairs = new HashSet<>();

        List<Submission> remaining = new ArrayList<>();
        remaining.addAll(submissions);

        while (remaining.size() >= 2) {
            // Get the first submission in the list and remove it
            Submission first = remaining.get(0);
            remaining.remove(0);

            // Form a pair for every remaining submission by pairing with the first, removed submission
            for (Submission submission : remaining) {
                Pair<Submission, Submission> pair = Pair.of(first, submission);
                Pair<Submission, Submission> reversed = Pair.of(submission, first);

                // Something's wrong, we've made a duplicate pair (but reversed)
                // Should never happen
                if (pairs.contains(reversed)) {
                    throw new RuntimeException("Internal error in pair generation: duplicate pair produced!");
                }

                // Add the newly-generated pair to our return
                pairs.add(pair);
            }
        }

        return pairs;
    }
}