💥 refactor(isPartitioned)!: Handle multiple pivots.

This fixes #65.

BREAKING CHANGE: This changes the API.

Author: make-github-pseudonymous-again

src/utils/firstInversion.js

@@ -6,16 +6,32 @@
  * @param {ArrayLike} array
  * @param {number} left
  * @param {number} right
- * @param {number} p
+ * @param {number[]} pivots
+ * @param {number} pi
+ * @param {number} pj
  * @return {number}
  */
-const firstInversion = (compare, array, left, right, p) => {
+const firstInversion = (compare, array, left, right, pivots, pi, pj) => {
+	let p = pivots[pi];
+	let x = array[p];
 	for (let k = left; k < p; ++k) {
-		if (compare(array[k], array[p]) > 0) return k;
+		if (compare(array[k], x) > 0) return k;
+	}
+
+	while (++pi < pj) {
+		const q = pivots[pi];
+		const y = array[q];
+		for (let k = p + 1; k < q; ++k) {
+			if (compare(array[k], x) < 0) return k;
+			if (compare(array[k], y) > 0) return k;
+		}
+
+		p = q;
+		x = y;
 	}
 
 	for (let k = p + 1; k < right; ++k) {
-		if (compare(array[k], array[p]) < 0) return k;
+		if (compare(array[k], x) < 0) return k;
 	}
 
 	return right;

src/utils/isPartitioned.js

@@ -8,10 +8,12 @@ import firstInversion from './firstInversion.js';
  * @param {ArrayLike} array
  * @param {number} left
  * @param {number} right
- * @param {number} p
+ * @param {number[]} pivots
+ * @param {number} pi
+ * @param {number} pj
  * @return {boolean}
  */
-const isPartitioned = (compare, array, left, right, p) =>
-	firstInversion(compare, array, left, right, p) === right;
+const isPartitioned = (compare, array, left, right, pivots, pi, pj) =>
+	firstInversion(compare, array, left, right, pivots, pi, pj) === right;
 
 export default isPartitioned;

test/src/isPartitioned.js

@@ -7,14 +7,14 @@ import {isPartitioned, firstInversion} from '../../src/index.js';
 const macro = (t, array, left, right, p, k1, k2) => {
 	const n = array.length;
 
-	t.true(firstInversion(increasing, array, left, right, p) === k1);
+	t.is(firstInversion(increasing, array, left, right, [p], 0, 1), k1);
 	if (k1 === right) {
-		t.true(isPartitioned(increasing, array, left, right, p));
+		t.true(isPartitioned(increasing, array, left, right, [p], 0, 1));
 	}
 
-	t.true(firstInversion(decreasing, array, left, right, p) === k2);
+	t.is(firstInversion(decreasing, array, left, right, [p], 0, 1), k2);
 	if (k2 === right) {
-		t.true(isPartitioned(decreasing, array, left, right, p));
+		t.true(isPartitioned(decreasing, array, left, right, [p], 0, 1));
 	}
 
 	t.is(array.length, n);
@@ -36,3 +36,9 @@ test(macro, [5, 4, 4, 5], 0, 4, 1, 0, 3);
 test(macro, [5, 4, 4, 5], 0, 4, 2, 0, 3);
 test(macro, [1, 0, 1, 1, 2, 3, 1, 0, 1], 3, 6, 4, 6, 3);
 test(macro, [1, 0, 1, 1, 2, 3, 1, 0, 1], 0, 9, 4, 6, 0);
+
+test('multi', (t) => {
+	const array = [0, 0, 0, 2, 2, 2, 4, 1, 3, 3, 3, 4];
+	t.is(firstInversion(increasing, array, 0, array.length, [4, 9], 0, 2), 6);
+	t.is(firstInversion(increasing, array, 0, array.length, [6, 9], 0, 2), 7);
+});

test/src/partition1.js

@@ -28,7 +28,7 @@ function check(partitionname, method, ctor, n, comparename, compare) {
 
 		// TEST PREDICATE
 
-		t.true(isPartitioned(compare, a, 0, n, p), 'check partitioned');
+		t.true(isPartitioned(compare, a, 0, n, [p], 0, 1), 'check partitioned');
 		t.is(a.length, n, 'check length a');
 	});
 }

test/src/partition2.js

@@ -32,8 +32,7 @@ function check(partitionname, method, ctor, n, comparename, compare) {
 		// TEST PREDICATE
 
 		t.true(p <= q, 'check p <= q');
-		t.true(isPartitioned(compare, a, 0, n, p), 'check partitioned p');
-		t.true(isPartitioned(compare, a, 0, n, q), 'check partitioned q');
+		t.true(isPartitioned(compare, a, 0, n, [p, q], 0, 2), 'check partitioned');
 		t.is(a.length, n, 'check length a');
 	});
 }

test/src/whole1.js

@@ -30,7 +30,7 @@ function check(partitionname, method, ctor, n, comparename, compare) {
 
 		// TEST PREDICATE
 
-		t.true(isPartitioned(compare, a, 0, n, p), 'check partitioned');
+		t.true(isPartitioned(compare, a, 0, n, [p], 0, 1), 'check partitioned');
 		t.is(a.length, n, 'check length a');
 	});
 }

test/src/whole2.js

@@ -34,8 +34,7 @@ function check(partitionname, method, ctor, n, comparename, compare) {
 		// TEST PREDICATE
 
 		t.true(p <= q, 'check p <= q');
-		t.true(isPartitioned(compare, a, 0, n, p), 'check partitioned p');
-		t.true(isPartitioned(compare, a, 0, n, q), 'check partitioned q');
+		t.true(isPartitioned(compare, a, 0, n, [p, q], 0, 2), 'check partitioned');
 		t.is(a.length, n, 'check length a');
 	});
 }