diff --git a/src/page-1/5. Longest Palindromic Substring/longestPalindrome.test.ts b/src/page-1/5. Longest Palindromic Substring/longestPalindrome.test.ts
new file mode 100644
index 0000000..a8160ea
--- /dev/null
+++ b/src/page-1/5. Longest Palindromic Substring/longestPalindrome.test.ts	
@@ -0,0 +1,8 @@
+import { longestPalindrome } from './longestPalindrome';
+
+describe('5. Longest Palindromic Substring', () => {
+  test('longestPalindrome', () => {
+    expect(longestPalindrome('babad')).toBe('aba');
+    expect(longestPalindrome('cbbd')).toBe('bb');
+  });
+});
diff --git a/src/page-1/5. Longest Palindromic Substring/longestPalindrome.ts b/src/page-1/5. Longest Palindromic Substring/longestPalindrome.ts
new file mode 100644
index 0000000..1dec7c6
--- /dev/null
+++ b/src/page-1/5. Longest Palindromic Substring/longestPalindrome.ts	
@@ -0,0 +1,48 @@
+type LongestPalindrome = (s: string) => string;
+
+/**
+ * Accepted
+ */
+export const longestPalindrome: LongestPalindrome = (s) => {
+  const n = s.length;
+
+  // If the string is empty or has only one character, it's itself a palindrome
+  if (n < 2) return s;
+
+  let start = 0; // Starting index of the longest palindromic substring
+  let maxLength = 1; // Length of the longest palindromic substring
+
+  // Initialize a 2D DP array
+  const dp: boolean[][] = Array.from({ length: n }, () => Array(n).fill(false));
+
+  // All substrings of length 1 are palindromes
+  for (let i = 0; i < n; i++) {
+    dp[i][i] = true;
+  }
+
+  // Check for substrings of length 2
+  for (let i = 0; i < n - 1; i++) {
+    if (s[i] === s[i + 1]) {
+      dp[i][i + 1] = true;
+      start = i;
+      maxLength = 2;
+    }
+  }
+
+  // Check for substrings of length greater than 2
+  for (let len = 3; len <= n; len++) {
+    for (let i = 0; i <= n - len; i++) {
+      // Ending index of substring
+      const j = i + len - 1;
+
+      if (s[i] === s[j] && dp[i + 1][j - 1]) {
+        dp[i][j] = true;
+        start = i;
+        maxLength = len;
+      }
+    }
+  }
+
+  // Extract the longest palindromic substring from start index and maxLength
+  return s.substring(start, start + maxLength);
+};
diff --git a/src/page-18/1880. Check if Word Equals Summation of Two Words/is-sum-equal.ts b/src/page-18/1880. Check if Word Equals Summation of Two Words/is-sum-equal.ts
deleted file mode 100644
index 75c2337..0000000
--- a/src/page-18/1880. Check if Word Equals Summation of Two Words/is-sum-equal.ts	
+++ /dev/null
@@ -1,11 +0,0 @@
-type IsSumEqual = (firstWord: string, secondWord: string, targetWord: string) => boolean;
-
-export const isSumEqual: IsSumEqual = (firstWord, secondWord, targetWord) => {
-  const sum = (str: string): number =>
-    Array.from(str).reduce((acc, cur) => Number(acc) + (cur.charCodeAt(0) - 'a'.charCodeAt(0)), 0);
-
-  const source = sum(firstWord) + sum(secondWord);
-  const target = sum(targetWord);
-
-  return source === target;
-};
diff --git a/src/page-18/1880. Check if Word Equals Summation of Two Words/is-sum-equal.test.ts b/src/page-18/1880. Check if Word Equals Summation of Two Words/isSumEqual.test.ts
similarity index 85%
rename from src/page-18/1880. Check if Word Equals Summation of Two Words/is-sum-equal.test.ts
rename to src/page-18/1880. Check if Word Equals Summation of Two Words/isSumEqual.test.ts
index e5ae176..0b691b8 100644
--- a/src/page-18/1880. Check if Word Equals Summation of Two Words/is-sum-equal.test.ts	
+++ b/src/page-18/1880. Check if Word Equals Summation of Two Words/isSumEqual.test.ts	
@@ -1,4 +1,4 @@
-import { isSumEqual } from './is-sum-equal';
+import { isSumEqual } from './isSumEqual';
 
 describe('1880. Check if Word Equals Summation of Two Words', () => {
   test('isSumEqual', () => {
diff --git a/src/page-18/1880. Check if Word Equals Summation of Two Words/isSumEqual.ts b/src/page-18/1880. Check if Word Equals Summation of Two Words/isSumEqual.ts
new file mode 100644
index 0000000..1c4bed5
--- /dev/null
+++ b/src/page-18/1880. Check if Word Equals Summation of Two Words/isSumEqual.ts	
@@ -0,0 +1,27 @@
+type IsSumEqual = (firstWord: string, secondWord: string, targetWord: string) => boolean;
+
+/**
+ * Accepted
+ */
+export const isSumEqual: IsSumEqual = (firstWord, secondWord, targetWord) => {
+  // Helper function to convert a word to its numerical value
+  function getNumericalValue(word: string): number {
+    let numericalString = '';
+
+    for (const char of word) {
+      // Convert char to its letter value by subtracting 'a' char code
+      numericalString += (char.charCodeAt(0) - 'a'.charCodeAt(0)).toString();
+    }
+
+    // Convert the concatenated string to a number
+    return Number.parseInt(numericalString, 10);
+  }
+
+  // Calculate numerical values for each word
+  const numFirstWord = getNumericalValue(firstWord);
+  const numSecondWord = getNumericalValue(secondWord);
+  const numTargetWord = getNumericalValue(targetWord);
+
+  // Check if the sum of numFirstWord and numSecondWord equals numTargetWord
+  return numFirstWord + numSecondWord === numTargetWord;
+};
diff --git a/src/page-18/1913. Maximum Product Difference Between Two Pairs/max-product-difference.test.ts b/src/page-18/1913. Maximum Product Difference Between Two Pairs/maxProductDifference.test.ts
similarity index 79%
rename from src/page-18/1913. Maximum Product Difference Between Two Pairs/max-product-difference.test.ts
rename to src/page-18/1913. Maximum Product Difference Between Two Pairs/maxProductDifference.test.ts
index 645507c..db0831f 100644
--- a/src/page-18/1913. Maximum Product Difference Between Two Pairs/max-product-difference.test.ts	
+++ b/src/page-18/1913. Maximum Product Difference Between Two Pairs/maxProductDifference.test.ts	
@@ -1,4 +1,4 @@
-import { maxProductDifference } from './max-product-difference';
+import { maxProductDifference } from './maxProductDifference';
 
 describe('1913. Maximum Product Difference Between Two Pairs', () => {
   test('maxProductDifference', () => {
diff --git a/src/page-18/1913. Maximum Product Difference Between Two Pairs/max-product-difference.ts b/src/page-18/1913. Maximum Product Difference Between Two Pairs/maxProductDifference.ts
similarity index 94%
rename from src/page-18/1913. Maximum Product Difference Between Two Pairs/max-product-difference.ts
rename to src/page-18/1913. Maximum Product Difference Between Two Pairs/maxProductDifference.ts
index 3ed4e7d..1bdfdd9 100644
--- a/src/page-18/1913. Maximum Product Difference Between Two Pairs/max-product-difference.ts	
+++ b/src/page-18/1913. Maximum Product Difference Between Two Pairs/maxProductDifference.ts	
@@ -1,6 +1,8 @@
 type MaxProductDifference = (nums: number[]) => number;
 
-// Accepted
+/**
+ * Accepted
+ */
 export const maxProductDifference: MaxProductDifference = (nums) => {
   const sorted = nums.sort((a, b) => b - a);
   const [max1, max2] = [sorted[0], sorted[1]];
diff --git a/src/page-21/2255. Count Prefixes of a Given String/count-prefixes.test.ts b/src/page-21/2255. Count Prefixes of a Given String/countPrefixes.test.ts
similarity index 82%
rename from src/page-21/2255. Count Prefixes of a Given String/count-prefixes.test.ts
rename to src/page-21/2255. Count Prefixes of a Given String/countPrefixes.test.ts
index 46a8147..ab27ea8 100644
--- a/src/page-21/2255. Count Prefixes of a Given String/count-prefixes.test.ts	
+++ b/src/page-21/2255. Count Prefixes of a Given String/countPrefixes.test.ts	
@@ -1,4 +1,4 @@
-import { countPrefixes } from './count-prefixes';
+import { countPrefixes } from './countPrefixes';
 
 describe('2255. Count Prefixes of a Given String', () => {
   test('countPrefixes', () => {
diff --git a/src/page-21/2255. Count Prefixes of a Given String/count-prefixes.ts b/src/page-21/2255. Count Prefixes of a Given String/countPrefixes.ts
similarity index 63%
rename from src/page-21/2255. Count Prefixes of a Given String/count-prefixes.ts
rename to src/page-21/2255. Count Prefixes of a Given String/countPrefixes.ts
index b759c23..90bc867 100644
--- a/src/page-21/2255. Count Prefixes of a Given String/count-prefixes.ts	
+++ b/src/page-21/2255. Count Prefixes of a Given String/countPrefixes.ts	
@@ -6,9 +6,8 @@ type CountPrefixes = (words: string[], s: string) => number;
 export const countPrefixes: CountPrefixes = (words, s) => {
   let count = 0;
 
-  for (let i = 0; i < words.length; i++) {
-    const cur = words[i];
-    if (s.startsWith(cur)) count += 1;
+  for (const word of words) {
+    if (s.startsWith(word)) count += 1;
   }
 
   return count;