Merge sort

src/merge-sort/index.js

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+function stitch(left, right) {
+  const results = [];
+  while (left.length && right.length) {
+    if (left[0] < right[0]) {
+      results.push(left.shift());
+    } else {
+      results.push(right.shift());
+    }
+  }
+
+  while (left.length) {
+    results.push(left.shift());
+  }
+
+  while (right.length) {
+    results.push(right.shift());
+  }
+
+  return results;
+}
+
+export const mergeSort = (arr) => {
+  const unsorted = arr;
+  if (unsorted.length < 2) {
+    return unsorted;
+  }
+
+  const length = unsorted.length;
+  const middle = Math.floor(length / 2);
+  const left = unsorted.slice(0, middle);
+  const right = unsorted.slice(middle, length);
+
+  return stitch(mergeSort(left), mergeSort(right));
+};

test/merge-sort.test.js

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+/**
+ * sorting-js
+ *
+ * Copyright © 2018 Neelesh Roy. All rights reserved.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE.txt file in the root directory of this source tree.
+ */
+
+import { expect } from 'chai';
+import { mergeSort } from '../src/merge-sort/index';
+
+
+describe('Merge Sort', () => {
+
+  describe('Merge Sort - function', () => {
+
+    it('should return empty array', () => {
+      const test = [];
+
+      const out = mergeSort(test);
+
+      expect(out).to.eql([]);
+    });
+
+    it('should sort the elements in ascending order', () => {
+      const test = [2, 5, 4, 10, 5, 3, 2, 7];
+
+      const out = mergeSort(test);
+
+      expect(out).to.eql([2, 2, 3, 4, 5, 5, 7, 10]);
+    });
+
+    it('should sort the string elements', () => {
+      const test = ['ayda', 'xsy', 'aaa', 'awb', 'cdf'];
+
+      const out = mergeSort(test);
+
+      expect(out).to.eql(['aaa', 'awb', 'ayda', 'cdf', 'xsy']);
+    });
+
+    it('should sort the floats elements', () => {
+      const test = [1.23, 9.78, 5.34, 3.45, 3.44];
+
+      const out = mergeSort(test);
+
+      expect(out).to.eql([1.23, 3.44, 3.45, 5.34, 9.78]);
+    });
+  });
+});