Add Fisher-Yates.

Author: trekhleb

README.md

@@ -33,10 +33,9 @@
   * [Power Set](https://github.com/trekhleb/javascript-algorithms/tree/master/src/algorithms/math/power-set)
   * [Primality Test](https://github.com/trekhleb/javascript-algorithms/tree/master/src/algorithms/math/primality-test) (trial division)
   * [Euclidean Algorithm](https://github.com/trekhleb/javascript-algorithms/tree/master/src/algorithms/math/euclidean-algorithm) - calculate the greatest common divisor (GCD)
+  * [Fisher–Yates Shuffle](https://github.com/trekhleb/javascript-algorithms/tree/master/src/algorithms/math/fisher-yates) - random permutation of a finite sequence
   * Collatz Conjecture algorithm
   * Extended Euclidean algorithm
-  * Find Divisors
-  * Fisher-Yates
   * Greatest Difference
   * Least Common Multiple
   * Newton's square

src/algorithms/math/fisher-yates/README.md

@@ -0,0 +1,15 @@
+# Fisher–Yates shuffle
+
+The Fisher–Yates shuffle is an algorithm for generating a random 
+permutation of a finite sequence—in plain terms, the algorithm 
+shuffles the sequence. The algorithm effectively puts all the 
+elements into a hat; it continually determines the next element 
+by randomly drawing an element from the hat until no elements 
+remain. The algorithm produces an unbiased permutation: every 
+permutation is equally likely. The modern version of the 
+algorithm is efficient: it takes time proportional to the 
+number of items being shuffled and shuffles them in place.
+
+## References
+
+[Wikipedia](https://en.wikipedia.org/wiki/Fisher%E2%80%93Yates_shuffle)

src/algorithms/math/fisher-yates/__test__/fisherYates.test.js

@@ -0,0 +1,19 @@
+import fisherYates from '../fisherYates';
+import { sortedArr } from '../../../sorting/SortTester';
+import QuickSort from '../../../sorting/quick-sort/QuickSort';
+
+describe('fisherYates', () => {
+  it('should shuffle small arrays', () => {
+    expect(fisherYates([])).toEqual([]);
+    expect(fisherYates([1])).toEqual([1]);
+  });
+
+  it('should shuffle array randomly', () => {
+    const shuffledArray = fisherYates(sortedArr);
+    const sorter = new QuickSort();
+
+    expect(shuffledArray.length).toBe(sortedArr.length);
+    expect(shuffledArray).not.toEqual(sortedArr);
+    expect(sorter.sort(shuffledArray)).toEqual(sortedArr);
+  });
+});

src/algorithms/math/fisher-yates/fisherYates.js

@@ -0,0 +1,21 @@
+/**
+ * @param {*[]} originalArray
+ * @return {*[]}
+ */
+export default function fisherYates(originalArray) {
+  // Clone array from preventing original array from modification (for testing purpose).
+  const array = originalArray.slice(0);
+
+  if (array.length <= 1) {
+    return array;
+  }
+
+  for (let i = (array.length - 1); i > 0; i -= 1) {
+    const randomIndex = Math.floor(Math.random() * (i + 1));
+    const tmp = array[randomIndex];
+    array[randomIndex] = array[i];
+    array[i] = tmp;
+  }
+
+  return array;
+}