feat: added js solution (and tests) for challenge longest-palindromic-substring

challenges/intermediate/longest-palindromic-substring/solutions/aleattene/solution.js

@@ -0,0 +1,66 @@
+/*
+JS solution for challenge: "Longest Palindromic Substring"
+To test the solution, type from CLI: npm test (required node.js and jest framework)
+*/
+
+
+function isPalindrome(word) {
+    // Shift indexes (left and right)
+    let i = 0;
+    let j = word.length - 1;
+    // Returns false as soon as two different values are found
+    while (i <= j) {
+        if (word[i] !== word[j]) {
+            // The number is not palindrome
+            return false;
+        }
+        i++; j--;
+    }
+    // The number is palindrome
+    return true;
+}
+
+
+function generateCombinations(word) {
+    // Array that will contain the combinations of characters/substrings
+    let combinations = [];
+    // Recursive function
+    let func = (prefix, word) => {
+        for (let i = 0; i < word.length; i++) {
+            combinations.push(prefix + word[i]);
+            // Recursive call
+            func(prefix + word[i], word.slice(i + 1));
+        }
+    }
+    // First call
+    func('', word);
+    return combinations;
+}
+
+
+function find_longest_palindromic_substring(word){
+    // Empty string
+    if (word === "") return "Sorry, you have entered an empty string."
+    // List of all combinations of characters present in the string, sorted by length (the longest at the top)
+    let combinations = generateCombinations(word).sort((w1, w2) => w2.length - w1.length);
+    // Start of search for the first longest palindrome string
+    let i = 0;
+    while (i < combinations.length) {
+        if (isPalindrome(combinations[i])) {
+            // palindrome substring found
+            return combinations[i]
+        }
+        i++;
+    }
+    // Check for a possible error
+    return "Warning, something went wrong."
+}
+
+
+
+// Exports for the tests
+module.exports = {
+    find_longest_palindromic_substring,
+}
+
+

challenges/intermediate/longest-palindromic-substring/solutions/aleattene/test.js

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+/*
+To start the tests, type from CLI: npm test (required node.js and jest framework)
+*/
+
+// Import Function to test
+const {find_longest_palindromic_substring} = require("./solution.js");
+
+// Tests
+test('Longest Palindromic Substring -  Unit Tests', () => {
+    expect(find_longest_palindromic_substring('babad')).toBe('bab');
+    expect(find_longest_palindromic_substring('cbbd')).toBe('bb');
+    expect(find_longest_palindromic_substring('a')).toBe('a');
+    expect(find_longest_palindromic_substring('ac')).toBe('a');
+    expect(find_longest_palindromic_substring('ale')).toBe('a');
+    expect(find_longest_palindromic_substring('1234321')).toBe('1234321');
+    expect(find_longest_palindromic_substring('')).toBe('Sorry, you have entered an empty string.');
+});