Add solution #5

Author: JoshCrozier

README.md

@@ -10,6 +10,7 @@
 2|[Add Two Numbers](./0002-add-two-numbers.js)|Medium|
 3|[Longest Substring Without Repeating Characters](./0003-longest-substring-without-repeating-characters.js)|Medium|
 4|[Median of Two Sorted Arrays](./0004-median-of-two-sorted-arrays.js)|Hard|
+5|[Longest Palindromic Substring](./0005-longest-palindromic-substring.js)|Medium|
 6|[ZigZag Conversion](./0006-zigzag-conversion.js)|Medium|
 7|[Reverse Integer](./0007-reverse-integer.js)|Easy|
 8|[String to Integer (atoi)](./0008-string-to-integer-atoi.js)|Medium|

solutions/0005-longest-palindromic-substring.js

@@ -0,0 +1,37 @@
+/**
+ * 5. Longest Palindromic Substring
+ * https://leetcode.com/problems/longest-palindromic-substring/
+ * Difficulty: Medium
+ *
+ * Given a string `s`, return the longest palindromic substring in `s`.
+ */
+
+/**
+ * @param {string} s
+ * @return {string}
+ */
+var longestPalindrome = function(s) {
+  let result = '';
+
+  for (let i = 0; i < s.length; i++) {
+    let palindrome1 = getExtendedPalindrome(s, i, i);
+    let palindrome2 = getExtendedPalindrome(s, i, i + 1);
+    let longerPalindrome = palindrome1.length > palindrome2.length
+      ? palindrome1 : palindrome2;
+
+    if (longerPalindrome.length > result.length) {
+      result = longerPalindrome;
+    }
+  }
+
+  return result;
+};
+
+function getExtendedPalindrome(s, start, end) {
+  while (start >= 0 && end < s.length && s[start] === s[end]) {
+    start--;
+    end++;
+  }
+
+  return s.slice(start + 1, end);
+}