feat(js): add modular solution and documentation for normal challenge 3 - Longest Unique Substring

Author: IbatoLionDev

2-NORMAL/JavaScript/3-longest-unique-substring/article.md

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+# Challenge Description and Solution
+
+## English Version
+
+### Challenge Description
+Given a string, find the length of the longest substring without repeating characters. Use sliding window techniques to optimize the solution's performance.
+
+### Code Explanation
+The solution uses a sliding window approach with two pointers (`left` and `right`) and a map to track the last index of each character. When a repeated character is found within the current window, the left pointer moves to the right of the previous occurrence to maintain a substring without duplicates.
+
+The function returns both the length and the longest substring without repeating characters.
+
+### Relevant Code Snippet
+
+```javascript
+class LongestUniqueSubstring {
+    static lengthOfLongestSubstring(s) {
+        const charIndexMap = new Map();
+        let left = 0;
+        let maxLength = 0;
+        let maxSubstring = "";
+
+        for (let right = 0; right < s.length; right++) {
+            if (charIndexMap.has(s[right]) && charIndexMap.get(s[right]) >= left) {
+                left = charIndexMap.get(s[right]) + 1;
+            }
+            charIndexMap.set(s[right], right);
+            if (right - left + 1 > maxLength) {
+                maxLength = right - left + 1;
+                maxSubstring = s.substring(left, right + 1);
+            }
+        }
+        return { maxLength, maxSubstring };
+    }
+}
+```
+
+### Example Usage
+
+```javascript
+import LongestUniqueSubstring from './longestUniqueSubstring.js';
+
+const testString = "abcabcbb";
+const { maxLength, maxSubstring } = LongestUniqueSubstring.lengthOfLongestSubstring(testString);
+console.log(`Length of longest substring without repeating characters: ${maxLength}`);
+console.log(`Longest substring without repeating characters: ${maxSubstring}`);
+```
+
+---
+
+## Versión en Español
+
+### Descripción del Reto
+Dada una cadena, encuentra la longitud de la subcadena más larga sin caracteres repetidos. Usa técnicas de ventana deslizante para optimizar el rendimiento de la solución.
+
+### Explicación del Código
+La solución utiliza un enfoque de ventana deslizante con dos punteros (`left` y `right`) y un mapa para rastrear el último índice de cada carácter. Cuando se encuentra un carácter repetido dentro de la ventana actual, el puntero izquierdo se mueve a la derecha de la ocurrencia previa para mantener una subcadena sin duplicados.
+
+La función retorna tanto la longitud como la subcadena más larga sin caracteres repetidos.
+
+### Fragmento de Código Relevante
+
+```javascript
+class LongestUniqueSubstring {
+    static lengthOfLongestSubstring(s) {
+        const charIndexMap = new Map();
+        let left = 0;
+        let maxLength = 0;
+        let maxSubstring = "";
+
+        for (let right = 0; right < s.length; right++) {
+            if (charIndexMap.has(s[right]) && charIndexMap.get(s[right]) >= left) {
+                left = charIndexMap.get(s[right]) + 1;
+            }
+            charIndexMap.set(s[right], right);
+            if (right - left + 1 > maxLength) {
+                maxLength = right - left + 1;
+                maxSubstring = s.substring(left, right + 1);
+            }
+        }
+        return { maxLength, maxSubstring };
+    }
+}
+```
+
+### Ejemplo de Uso
+
+```javascript
+import LongestUniqueSubstring from './longestUniqueSubstring.js';
+
+const testString = "abcabcbb";
+const { maxLength, maxSubstring } = LongestUniqueSubstring.lengthOfLongestSubstring(testString);
+console.log(`Longitud de la subcadena más larga sin caracteres repetidos: ${maxLength}`);
+console.log(`Subcadena más larga sin caracteres repetidos: ${maxSubstring}`);

2-NORMAL/JavaScript/3-longest-unique-substring/proposed-solution/longestUniqueSubstring.js

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+// longestUniqueSubstring.js - Implementation of longest unique substring using sliding window technique
+
+class LongestUniqueSubstring {
+    static lengthOfLongestSubstring(s) {
+        const charIndexMap = new Map();
+        let left = 0;
+        let maxLength = 0;
+        let maxSubstring = "";
+
+        for (let right = 0; right < s.length; right++) {
+            if (charIndexMap.has(s[right]) && charIndexMap.get(s[right]) >= left) {
+                left = charIndexMap.get(s[right]) + 1;
+            }
+            charIndexMap.set(s[right], right);
+            if (right - left + 1 > maxLength) {
+                maxLength = right - left + 1;
+                maxSubstring = s.substring(left, right + 1);
+            }
+        }
+        return { maxLength, maxSubstring };
+    }
+}
+
+export default LongestUniqueSubstring;

2-NORMAL/JavaScript/3-longest-unique-substring/proposed-solution/main.js

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+/*
+Challenge: Given a string, find the length of the longest substring without repeating characters.
+Use sliding window techniques to optimize the solution's performance.
+*/
+
+// main.js - Example usage of LongestUniqueSubstring
+
+import LongestUniqueSubstring from './longestUniqueSubstring.js';
+
+
+function main() {
+    const testString = "abcabcbb";
+    const { maxLength, maxSubstring } = LongestUniqueSubstring.lengthOfLongestSubstring(testString);
+    console.log(`Length of longest substring without repeating characters: ${maxLength}`);
+    console.log(`Longest substring without repeating characters: ${maxSubstring}`);
+}
+
+main();