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/*
* SPDX-FileCopyrightText: 2023 The Refinery Authors <https://refinery.tools/>
*
* SPDX-License-Identifier: EPL-2.0
*/
package tools.refinery.store.statecoding.stateequivalence;
import java.util.ArrayList;
import java.util.List;
class CombinationNodePairingPermutations {
private final List<List<int[]>> permutations = new ArrayList<>();
public CombinationNodePairingPermutations(int max) {
initializePermutations(max);
}
public List<int[]> getPermutations(int max) {
if (max >= permutations.size()) {
throw new IllegalArgumentException("Only permutations up to %d elements are supported".formatted(max));
}
return permutations.get(max);
}
/**
* Generates and stores permutations up to a given size. If the number would be more than a limit, it provides a
* single permutation only.
*
* @param max The max number in the permutation
* @return A complete list of permutations of numbers 0...max, or a single permutation.
*/
private List<int[]> initializePermutations(int max) {
if (max < permutations.size()) {
return permutations.get(max);
}
if (max == 0) {
List<int[]> result = new ArrayList<>();
result.add(new int[1]);
permutations.add(result);
return result;
}
List<int[]> result = new ArrayList<>();
List<int[]> previousPermutations = initializePermutations(max - 1);
for (var permutation : previousPermutations) {
for (int pos = 0; pos <= max; pos++) {
int[] newPermutation = new int[max + 1];
System.arraycopy(permutation, 0, newPermutation, 0, pos);
newPermutation[pos] = max;
if (max - (pos + 1) >= 0)
System.arraycopy(permutation, pos + 1, newPermutation, pos + 1 + 1, max - (pos + 1));
result.add(newPermutation);
}
}
permutations.add(result);
return result;
}
}
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