com.topekalabs.algos.discrete.Permutations.java Source code

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Here is the source code for com.topekalabs.algos.discrete.Permutations.java

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/*
 * Copyright 2015 Topeka Labs.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.topekalabs.algos.discrete;

import com.google.common.collect.Maps;
import com.google.common.collect.Sets;
import com.topekalabs.collection.utils.CollectionUtils;
import java.util.Map;
import java.util.Set;

/**
 *
 * @author Topeka Labs
 */
public final class Permutations {
    private Permutations() {
    }

    public static <L, V> Set<Map<L, V>> labeledPermutations(Map<L, Set<V>> valuesMap) {
        Set<Map<L, V>> permutations = Sets.newHashSet();

        if (valuesMap.isEmpty()) {
            return permutations;
        }

        Map.Entry<L, Set<V>> mapEntry = CollectionUtils.getSingleElement(valuesMap.entrySet());
        L label = mapEntry.getKey();
        Set<V> values = mapEntry.getValue();

        if (valuesMap.size() == 1) {
            for (V value : values) {
                Map<L, V> permutation = Maps.newHashMap();
                permutation.put(label, value);
                permutations.add(permutation);
            }

            return permutations;
        }

        Map<L, Set<V>> reducedValuesMap = Maps.newHashMap(valuesMap);
        reducedValuesMap.remove(label);

        Set<Map<L, V>> reducedPermutations = labeledPermutations(reducedValuesMap);

        for (Map<L, V> reducedPermutation : reducedPermutations) {
            for (V value : values) {
                Map<L, V> permutation = Maps.newHashMap(reducedPermutation);
                permutation.put(label, value);
                permutations.add(permutation);
            }
        }

        return permutations;
    }
}