1 files changed, 57 insertions, 0 deletions

diff --git a/subprojects/store/src/main/java/tools/refinery/store/statecoding/stateequivalence/CombinationNodePairingPermutations.java b/subprojects/store/src/main/java/tools/refinery/store/statecoding/stateequivalence/CombinationNodePairingPermutations.java
new file mode 100644
index 00000000..eacd3a2a
--- /dev/null
+++ b/subprojects/store/src/main/java/tools/refinery/store/statecoding/stateequivalence/CombinationNodePairingPermutations.java
@@ -0,0 +1,57 @@
+/*
+ * 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;
+        }
+}