Merge pull request #131 from jeantimex/permutations

feat(backtracking): Permutations

Author: jeantimex

README.md

@@ -109,6 +109,7 @@ A collection of JavaScript problems and solutions for studying algorithms.
 - [Combination Sum](src/backtracking/combination-sum.js)
 - [Combination Sum II](src/backtracking/combination-sum-ii.js)
 - [Combination Sum III](src/backtracking/combination-sum-iii.js)
+- [Permutations](src/backtracking/permutations.js)
 
 ### Linked List
 

src/backtracking/__tests__/permutations-test.js

@@ -0,0 +1,22 @@
+import { assert } from 'chai';
+import permute from '../permutations';
+
+const sorter = (a, b) => {
+  if (a.length === b.length) {
+    return a.toString().localeCompare(b.toString());
+  }
+  return a.length - b.length;
+};
+
+describe('Permutations', () => {
+  const testCases = [[[1, 2, 3], [[1, 2, 3], [1, 3, 2], [2, 1, 3], [2, 3, 1], [3, 1, 2], [3, 2, 1]]]];
+
+  testCases.forEach((testCase, index) => {
+    it(`should get the permutations using back tracking ${index}`, () => {
+      const nums = testCase[0];
+      const expected = testCase[1];
+      const actual = permute(nums);
+      assert(actual.sort(sorter), expected.sort(sorter));
+    });
+  });
+});

src/backtracking/permutations.js

@@ -0,0 +1,47 @@
+/**
+ * Permutations
+ *
+ * Given a collection of distinct numbers, return all possible permutations.
+ *
+ * For example,
+ * [1,2,3] have the following permutations:
+ * [
+ *   [1,2,3],
+ *   [1,3,2],
+ *   [2,1,3],
+ *   [2,3,1],
+ *   [3,1,2],
+ *   [3,2,1]
+ * ]
+ */
+
+/**
+ * @param {number[]} nums
+ * @return {number[][]}
+ */
+const permute = nums => {
+  const results = [];
+  backtracking(nums, {}, [], results);
+  return results;
+};
+
+const backtracking = (nums, used, solution, results) => {
+  if (solution.length === nums.length) {
+    results.push(solution.slice());
+    return;
+  }
+
+  for (let i = 0; i < nums.length; i++) {
+    if (used[i]) {
+      continue;
+    }
+
+    solution.push(nums[i]);
+    used[i] = true;
+    backtracking(nums, used, solution, results);
+    solution.pop();
+    used[i] = false;
+  }
+};
+
+export default permute;