Added medium/permutation_step

Author: bradhanson

medium/permutation_step.js

@@ -0,0 +1,63 @@
+/**
+ * Have the function permutationStep(num) take the num parameter being passed
+ * and return the next number greater than num using the same digits. For
+ * example: if num is 123 return 132, if it's 12453 return 12534. If a number
+ * has no greater permutations, return -1 (ie. 999).
+ *
+ * https://www.coderbyte.com/results/bhanson:Permutation%20Step:JavaScript
+ *
+ * @param {number} num
+ * @return {number}
+ */
+function permutationStep(num) {
+ const permutations = Array.from(
+ new Set( // use Set to filter for unique values
+ permute(num.toString().split(''))
+ .map(number => number.join(''))
+ .map(Number)
+ )
+ );
+
+ permutations.sort((a, b) => a - b);
+
+ const largerPermutations = permutations.filter(
+ permutation => permutation > num
+ );
+
+ if (largerPermutations.length > 0) {
+ return largerPermutations[0];
+ }
+ return -1;
+}
+
+// https://en.wikipedia.org/wiki/Heap's_algorithm
+// Iterative
+function permute(arr) {
+ let count = Array(arr.length).fill(0);
+
+ const results = [arr.slice()];
+
+ let i = 0;
+ while (i < arr.length) {
+ if (count[i] < i) {
+ if (i % 2 === 0) {
+ const temp = arr[0];
+ arr[0] = arr[i];
+ arr[i] = temp;
+ } else {
+ const temp = arr[count[i]];
+ arr[count[i]] = arr[i];
+ arr[i] = temp;
+ }
+ results.push(arr.slice());
+ count[i]++;
+ i = 0;
+ } else {
+ count[i] = 0;
+ i++;
+ }
+ }
+ return results;
+}
+
+module.exports = permutationStep;

medium/permutation_step.test.js

@@ -0,0 +1,25 @@
+const permutationStep = require('./permutation_step');
+
+describe('permutationStep()', () => {
+ test('passes Coderbyte.com tests', () => {
+ expect(permutationStep(11121)).toBe(11211);
+
+ expect(permutationStep(41352)).toBe(41523);
+
+ expect(permutationStep(456)).toBe(465);
+
+ expect(permutationStep(111)).toBe(-1);
+
+ expect(permutationStep(23514)).toBe(23541);
+
+ expect(permutationStep(897654321)).toBe(912345678);
+
+ expect(permutationStep(12)).toBe(21);
+
+ expect(permutationStep(9)).toBe(-1);
+
+ expect(permutationStep(44444444)).toBe(-1);
+
+ expect(permutationStep(76666666)).toBe(-1);
+ });
+});