From 8d79125bd46d21c71f4cc9276d16bcd9d5a3a3e4 Mon Sep 17 00:00:00 2001
From: FeschenkoNatalia <natalia141277.nf@gmail.com>
Date: Fri, 6 Apr 2018 11:43:32 +0300
Subject: [PATCH] Fix merge sort

---
 lib/sorts/merge-sort/index.js           | 30 +++++++++++++++++++++++++
 lib/sorts/merge-sort/merge-sort.test.js | 18 +++++++++++++++
 2 files changed, 48 insertions(+)
 create mode 100644 lib/sorts/merge-sort/index.js
 create mode 100644 lib/sorts/merge-sort/merge-sort.test.js

diff --git a/lib/sorts/merge-sort/index.js b/lib/sorts/merge-sort/index.js
new file mode 100644
index 0000000..08473ee
--- /dev/null
+++ b/lib/sorts/merge-sort/index.js
@@ -0,0 +1,30 @@
+function merge(left, right) {
+    const result = [];
+    while (left.length && right.length) {
+        if (left[0] <= right[0]) {
+            result.push(left.shift());
+        } else {
+            result.push(right.shift());
+        }
+    }
+    while (left.length) {
+        result.push(left.shift());
+    }
+
+    while (right.length) {
+        result.push(right.shift());
+    }
+    return result;
+}
+
+module.exports = function mergeSort(array) {
+    if (array.length === 0 || array.length < 2) {
+        return array;
+    }
+    const middle = Math.floor(array.length / 2);
+    const left = array.slice(0, middle);
+    const right = array.slice(middle, array.length);
+
+    return merge(mergeSort(left), mergeSort(right));
+};
+
diff --git a/lib/sorts/merge-sort/merge-sort.test.js b/lib/sorts/merge-sort/merge-sort.test.js
new file mode 100644
index 0000000..19d5e96
--- /dev/null
+++ b/lib/sorts/merge-sort/merge-sort.test.js
@@ -0,0 +1,18 @@
+
+const should = require('should');
+const algo = require('../../index.js');
+
+describe('Merge sort', () => {
+    it('should return empty array when empty array was passed', () => {
+        const array = algo.mergeSort([]);
+        should(array).be.eql([]);
+    });
+    it('should return sorted array if sorted array was passed', () => {
+        const array = algo.mergeSort([0, 1, 2, 3, 5]);
+        should(array).be.eql([0, 1, 2, 3, 5]);
+    });
+    it('should return sorted array if any not empty array was passed', () => {
+        const array = algo.mergeSort([9, 11, 2, 31, 7]);
+        should(array).be.eql([2, 7, 9, 11, 31]);
+    });
+});