From 7aa9410c7a722ee60d65d5d9f9381d5bd89b8727 Mon Sep 17 00:00:00 2001
From: piemme <paolomanca@gmail.com>
Date: Sun, 11 Oct 2020 19:00:38 +0200
Subject: [PATCH] Add Algorithm String Permutation

---
 String/PermutateString.js      | 33 +++++++++++++++++++++++++++++++++
 String/PermutateString.test.js | 17 +++++++++++++++++
 2 files changed, 50 insertions(+)
 create mode 100644 String/PermutateString.js
 create mode 100644 String/PermutateString.test.js

diff --git a/String/PermutateString.js b/String/PermutateString.js
new file mode 100644
index 0000000000..e470d7ac35
--- /dev/null
+++ b/String/PermutateString.js
@@ -0,0 +1,33 @@
+'use strict'
+
+const permutate = (aString) => {
+  if (typeof aString !== 'string' || !aString) {
+    throw new Error('The arg must be a valid, non empty string')
+  }
+  const characters = aString.split('')
+  let permutations = [[characters.shift()]]
+  while (characters.length) {
+    const currentCharacter = characters.shift()
+    permutations = calculateCurrentCharacterPermutation(permutations, currentCharacter)
+  }
+  return permutations
+    .map(character => character.join(''))
+    .filter((item, index, self) => (self.indexOf(item) === index))
+    .sort()
+}
+
+const calculateCurrentCharacterPermutation = (allPermutations, currentCharacter) => {
+  const currentPermutations = []
+  allPermutations.map(permutation => {
+    let index = 0
+    while (index <= permutation.length) {
+      const tmp = [...permutation]
+      tmp.splice(index, 0, currentCharacter)
+      currentPermutations.push(tmp)
+      index++
+    }
+  })
+  return currentPermutations
+}
+
+export { permutate }
diff --git a/String/PermutateString.test.js b/String/PermutateString.test.js
new file mode 100644
index 0000000000..71df87b5eb
--- /dev/null
+++ b/String/PermutateString.test.js
@@ -0,0 +1,17 @@
+import { permutate } from './PermutateString'
+
+describe('Permutate a string', () => {
+  it('expects to throw an Error with an empty string', () => {
+    expect(() => { permutate() }).toThrow('The arg must be a valid, non empty string')
+  })
+  it('expects to permute "no" into [no, on]', () => {
+    expect(['no', 'on']).toEqual(permutate('no'))
+  })
+  it('expects to permute "yes" into [esy, eys, sey, sye, yes, yse]', () => {
+    expect(['esy', 'eys', 'sey', 'sye', 'yes', 'yse']).toEqual(permutate('yes'))
+  })
+  it('expects to permute "good" into [dgoo dogo doog gdoo godo good odgo odog ogdo ogod oodg oogd ]', () => {
+    expect(['dgoo', 'dogo', 'doog', 'gdoo', 'godo', 'good', 'odgo', 'odog', 'ogdo', 'ogod', 'oodg', 'oogd'])
+      .toEqual(permutate('good'))
+  })
+})