From 344838c30ed59161bab9fb9a6af221779accd10a Mon Sep 17 00:00:00 2001
From: zhabinka <sergeykarpuk@yandex.by>
Date: Wed, 9 Jan 2019 00:44:29 +0300
Subject: [PATCH] Added Run Length Encoding

---
 .../run-length-encoding.js                    | 32 ++++++++++
 .../run-length-encoding.spec.js               | 59 +++++++++++++++++++
 2 files changed, 91 insertions(+)
 create mode 100644 javascript/run-length-encoding/run-length-encoding.js
 create mode 100644 javascript/run-length-encoding/run-length-encoding.spec.js

diff --git a/javascript/run-length-encoding/run-length-encoding.js b/javascript/run-length-encoding/run-length-encoding.js
new file mode 100644
index 0000000..ac6a676
--- /dev/null
+++ b/javascript/run-length-encoding/run-length-encoding.js
@@ -0,0 +1,32 @@
+const encode = (str) => {
+  const iter = (s, arr) => {
+    if (s.length === 0) {
+      return arr;
+    }
+    const regex = new RegExp(`${s[0]}+`);
+    const charsGroup = s.match(regex)[0];
+
+    return iter(s.substr(charsGroup.length), arr.concat(charsGroup));
+  };
+
+  const groups = iter(str, []);
+
+  return groups
+    .map(el => (el.length === 1 ? el : `${el.length}${el[0]}`))
+    .join('');
+};
+
+
+const decode = (str) => {
+  if (str === '') {
+    return str;
+  }
+
+  return str
+    .match(/\d*.{1}/g)
+    .map(el => (el.length > 1 ? el : `1${el}`))
+    .map(el => el.slice(-1).repeat(el.match(/\d*/)))
+    .join('');
+};
+
+export { encode, decode };
diff --git a/javascript/run-length-encoding/run-length-encoding.spec.js b/javascript/run-length-encoding/run-length-encoding.spec.js
new file mode 100644
index 0000000..c0d6da2
--- /dev/null
+++ b/javascript/run-length-encoding/run-length-encoding.spec.js
@@ -0,0 +1,59 @@
+import { encode, decode } from './run-length-encoding';
+
+describe('run-length encode a string', () => {
+  test('encode empty string', () => {
+    expect(encode('')).toEqual('');
+  });
+
+  test('single characters only are encoded without count', () => {
+    expect(encode('XYZ')).toEqual('XYZ');
+  });
+
+  test('encode string with no single characters', () => {
+    expect(encode('AABBBCCCC')).toEqual('2A3B4C');
+  });
+
+  test('encode string with single characters mixed with repeated characters', () => {
+    expect(encode('WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWB')).toEqual('12WB12W3B24WB');
+  });
+
+  test('encode string with multiple whitespaces', () => {
+    expect(encode('  hsqq qww  ')).toEqual('2 hs2q q2w2 ');
+  });
+
+  test('encode string with lowercase characters', () => {
+    expect(encode('aabbbcccc')).toEqual('2a3b4c');
+  });
+});
+
+describe('run-length decode a string', () => {
+  test('decode empty string', () => {
+    expect(decode('')).toEqual('');
+  });
+
+  test('decode string with single characters only', () => {
+    expect(decode('XYZ')).toEqual('XYZ');
+  });
+
+  test('decode string with no single characters', () => {
+    expect(decode('2A3B4C')).toEqual('AABBBCCCC');
+  });
+
+  test('decode string with single characters mixed with repeated characters', () => {
+    expect(decode('12WB12W3B24WB')).toEqual('WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWB');
+  });
+
+  test('decode string with multiple whitespaces', () => {
+    expect(decode('2 hs2q q2w2 ')).toEqual('  hsqq qww  ');
+  });
+
+  test('decode string with lowercase characters', () => {
+    expect(decode('2a3b4c')).toEqual('aabbbcccc');
+  });
+});
+
+describe('run-length encode and then decode', () => {
+  test('encode followed by decode gives original string', () => {
+    expect(decode(encode('zzz ZZ  zZ'))).toEqual('zzz ZZ  zZ');
+  });
+});