Implement the 'string compression' algorithm

Author: FSou1

README.md

@@ -30,6 +30,7 @@ An algorithm is a finite sequence of well-defined, computer-implementable instru
   * [Is unique](src/algorithms/string/unique) - check a string for uniqueness;
   * [Check permutation](src/algorithms/string/permutation) - check if a string is a permutation of the other;
   * [URLify](src/algorithms/string/urlify) - replace all spaces in a string with '%20';
+  * [String compression](src/algorithms/string/compression) - perform basic string compression using the counts of repeated characters;
 * **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/compression/README.md

@@ -0,0 +1,7 @@
+# String compression
+
+Implement a method to perform basic string compression using the counts of repeated characters.
+
+For example, the string aabcccccaaa would become a2blc5a3. If the "compressed" string would not become smaller than the original string, your method should return the original string. 
+
+You can assume the string has only uppercase and lowercase letters (a - z). 

src/algorithms/string/compression/__test__/compression.test.ts

@@ -0,0 +1,8 @@
+import { compression } from "../compression";
+
+test.each([
+  ["aabcccccaaa", "a2b1c5a3"],
+  ["abcde", "abcde"]
+])("the compressed value of the string '%p' is '%p'", (input, output) => {
+  expect(compression(input)).toBe(output);
+});

src/algorithms/string/compression/compression.ts

@@ -0,0 +1,25 @@
+/**
+ * A method to perform basic string compression using the counts of repeated characters.
+ * - The string aabcccccaaa would become a2blc5a3;
+ * - If the "compressed" string is not smaller than the original one, the method returns the original string.
+ * @param  {string} input
+ * @returns string
+ */
+export function compression(input: string): string {
+  const len = input.length;
+  const output = [];
+
+  let counter = 1;
+  for (let i = 0; i < len; i++) {
+    if (input[i] === input[i + 1]) {
+      counter++;
+    } else {
+      output.push(input[i], counter);
+      counter = 1;
+    }
+  }
+
+  const result = output.join("");
+
+  return result.length > len ? input : result;
+}