Upstream simple-statistics/simple-statistics state of the touched files before afe3d20779

src/permutations_heap.js

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+/**
+ * Implementation of [Heap's Algorithm](https://en.wikipedia.org/wiki/Heap%27s_algorithm)
+ * for generating permutations.
+ *
+ * @param {Array} elements any type of data
+ * @returns {Array<Array>} array of permutations
+ */
+function permutationsHeap(elements) {
+    const indexes = new Array(elements.length);
+    const permutations = [elements.slice()];
+
+    for (let i = 0; i < elements.length; i++) {
+        indexes[i] = 0;
+    }
+
+    for (let i = 0; i < elements.length; ) {
+        if (indexes[i] < i) {
+            // At odd indexes, swap from indexes[i] instead
+            // of from the beginning of the array
+            let swapFrom = 0;
+            if (i % 2 !== 0) {
+                swapFrom = indexes[i];
+            }
+
+            // swap between swapFrom and i, using
+            // a temporary variable as storage.
+            const temp = elements[swapFrom];
+            elements[swapFrom] = elements[i];
+            elements[i] = temp;
+
+            permutations.push(elements.slice());
+            indexes[i]++;
+            i = 0;
+        } else {
+            indexes[i] = 0;
+            i++;
+        }
+    }
+
+    return permutations;
+}
+
+export default permutationsHeap;

test/permutations_heap.test.js

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+import assert from "node:assert/strict";
+import { describe, it } from "node:test";
+import * as ss from "../index.js";
+
+describe("permutationsHeap", function () {
+    it("generates 1 permutation", function () {
+        assert.deepEqual(ss.permutationsHeap([1]), [[1]]);
+    });
+    it("generates 1, 2, 3 permutations", function () {
+        assert.deepEqual(ss.permutationsHeap([1, 2, 3]), [
+            [1, 2, 3],
+            [2, 1, 3],
+            [3, 1, 2],
+            [1, 3, 2],
+            [2, 3, 1],
+            [3, 2, 1]
+        ]);
+    });
+});