Add two implementations of the 'is unique' algorithm

Author: FSou1

README.md

@@ -27,6 +27,7 @@ An algorithm is a finite sequence of well-defined, computer-implementable instru
   * [Binary search](src/algorithms/search/binary) - find a position of the element in a sorted one-dimensional array;
 * **String**
   * [Document distance](src/algorithms/string/document-distance) - measure similarity between two strings;
+  * [Is unique](src/algorithms/string/unique) - check a string for uniqueness;
 * **Sort**
   * [Insertion sort](src/algorithms/sort/insertion/simple) - sort an array with a simple insertion algorithm;
   * [Merge sort](src/algorithms/sort/merge) - sort an array with a merge sort algorithm;

src/algorithms/string/unique/README.md

@@ -0,0 +1,11 @@
+# Is Unique
+
+Implement an algorithm to determine if a string has all unique characters. What if you cannot use additional data structures?
+
+## uniqueV1
+
+This algorithm uses additional memory which gives you `O(n)` time and `O(n)` memory.
+
+## uniqueV2
+
+This algorithm does not use additional memory but alters the input. This one gives you `O(n * log n)` time (depends on the sorting algorithm you choose).

src/algorithms/string/unique/__tests__/unique.test.ts

@@ -0,0 +1,20 @@
+import { uniqueV1 } from "../uniqueV1";
+import { uniqueV2 } from "../uniqueV2";
+
+test.each([
+  ["abc", true],
+  ["aab", false],
+  ["abcdefghijklmnopqrstuvwxyz123456789a", false],
+  ["abcdefghijklmnopqrst uvwxyz123456789ABCDEFGHJ0_!';,.", true]
+])("#1 the string %p has unique characters only: %p", (input, value) => {
+  expect(uniqueV1(input)).toBe(value);
+});
+
+test.each([
+  ["abc", true],
+  ["aab", false],
+  ["abcdefghijklmnopqrstuvwxyz123456789a", false],
+  ["abcdefghijklmnopqrst uvwxyz123456789ABCDEFGHJ0_!';,.", true]
+])("#2 the string %p has unique characters only: %p", (input, value) => {
+  expect(uniqueV2(input)).toBe(value);
+});

src/algorithms/string/unique/uniqueV1.ts

@@ -0,0 +1,19 @@
+/**
+ * Check if the input has unique characters only
+ *  - Time complexity: O(n)
+ *  - Memory complexity: O(n)
+ * @param  {string} input
+ * @returns boolean
+ */
+export function uniqueV1(input: string): boolean {
+  const dict = {};
+  for (const char of input) {
+    if (dict[char]) {
+      return false;
+    }
+
+    dict[char] = 1;
+  }
+
+  return true;
+}

src/algorithms/string/unique/uniqueV2.ts

@@ -0,0 +1,17 @@
+import { sort } from "../../sort/heap/heapSort";
+
+/**
+ * Check if the input has unique characters only
+ *  - Time complexity: O(n * log n)
+ * @param  {string} input
+ * @returns boolean
+ */
+export function uniqueV2(input: string): boolean {
+  const sorted = sort(input.split("").map((s) => s.charCodeAt(0)));
+  for (let i = 0, j = sorted.length - 1; i < j; i++) {
+    if (sorted[i] === sorted[i + 1]) {
+      return false;
+    }
+  }
+  return true;
+}