add: RunLengthEncoding function implementation

Author: EliasAfara

DIRECTORY.md

@@ -29,3 +29,4 @@
 - **Strings**
  - [CaesarCipherEncryptor](Strings/CaesarCipherEncryptor.js)
  - [PalindromeCheck](Strings/PalindromeCheck.js)
+ - [RunLengthEncoding](Strings/RunLengthEncoding.js)

Strings/RunLengthEncoding.js

@@ -0,0 +1,35 @@
+/**
+ * Encodes a given string using run-length encoding.
+ *
+ * Run-length encoding is a lossless data compression technique where runs of
+ * consecutive identical characters are replaced with a count and the character itself.
+ *
+ * @param {string} string - The input string to be encoded.
+ * @returns {string} - The run-length encoded string.
+ *
+ * @example
+ * const input = "AAAAAAAAAAAAABBCCCCDD";
+ * const encodedString = runLengthEncoding(input); // Output: "9A4A2B4C2D"
+ *
+ * @complexity
+ * Time Complexity: O(n), where n is the length of the input string. We iterate through the string once.
+ * Space Complexity: O(m), where m is the length of the encoded string. In the worst case, each character is encoded separately.
+ */
+function runLengthEncoding(string) {
+ let encoded = [];
+ let run = 1;
+
+ for (let i = 0; i < string.length; i++) {
+ let letter = string[i];
+ if (letter === string[i + 1] && run < 9) {
+ run++;
+ } else {
+ encoded.push(`${run}${letter}`);
+ run = 1;
+ }
+ }
+
+ return encoded.join("");
+}
+
+export { runLengthEncoding };

Strings/tests/RunLengthEncoding.test.js

@@ -0,0 +1,66 @@
+import { runLengthEncoding } from "../RunLengthEncoding";
+
+describe("runLengthEncoding", () => {
+ it("should encode a string with consecutive characters correctly", () => {
+ const input = "AAABBBCCCDDEE";
+ const expectedOutput = "3A3B3C2D2E";
+ const encodedString = runLengthEncoding(input);
+ expect(encodedString).toBe(expectedOutput);
+ });
+
+ it("should handle single characters without encoding", () => {
+ const input = "aA";
+ const expectedOutput = "1a1A";
+ const encodedString = runLengthEncoding(input);
+ expect(encodedString).toBe(expectedOutput);
+ });
+
+ it("should handle special characters", () => {
+ const input = "!@##$$$";
+ const expectedOutput = "1!1@2#3$";
+ const encodedString = runLengthEncoding(input);
+ expect(encodedString).toBe(expectedOutput);
+ });
+
+ it("should handle a mix of characters", () => {
+ const input = "AABBB!@";
+ const expectedOutput = "2A3B1!1@";
+ const encodedString = runLengthEncoding(input);
+ expect(encodedString).toBe(expectedOutput);
+ });
+
+ it("should handle a string of consecutive numbers", () => {
+ const input = "122333";
+ const expectedOutput = "112233";
+ const encodedString = runLengthEncoding(input);
+ expect(encodedString).toBe(expectedOutput);
+ });
+
+ it("should handle a string of consecutive special characters", () => {
+ const input = "************^^^^^^^$$$$$$%%%%%%%!!!!!!AAAAAAAAAAAAAAAAAAAA";
+ const expectedOutput = "9*3*7^6$7%6!9A9A2A";
+ const encodedString = runLengthEncoding(input);
+ expect(encodedString).toBe(expectedOutput);
+ });
+
+ it("should handle a mix of lowercase, uppercase, and numbers", () => {
+ const input = "aAaAaaaaaAaaaAAAABbbbBBBB";
+ const expectedOutput = "1a1A1a1A5a1A3a4A1B3b4B";
+ const encodedString = runLengthEncoding(input);
+ expect(encodedString).toBe(expectedOutput);
+ });
+
+ it("should handle an empty string", () => {
+ const input = "";
+ const expectedOutput = "";
+ const encodedString = runLengthEncoding(input);
+ expect(encodedString).toBe(expectedOutput);
+ });
+
+ it("should handle a string with spaces and numbers", () => {
+ const input = "1 222 333 444 555";
+ const expectedOutput = "112 321 334 342 35";
+ const encodedString = runLengthEncoding(input);
+ expect(encodedString).toBe(expectedOutput);
+ });
+});