Add Leetcode #5 solution (#66)

Co-authored-by: Chi Hi Ong <[email protected]>

Author: ongzx

JavaScript/5.Longest-Palindromic-Substring.js

@@ -0,0 +1,54 @@
+/**
+ * Given a string s, return the longest palindromic substring in s.
+ * 
+ * Example 1:
+
+Input: s = "babad"
+Output: "bab"
+Note: "aba" is also a valid answer.
+Example 2:
+
+Input: s = "cbbd"
+Output: "bb"
+Example 3:
+
+Input: s = "a"
+Output: "a"
+Example 4:
+
+Input: s = "ac"
+Output: "a"
+ 
+
+Constraints:
+
+1 <= s.length <= 1000
+s consist of only digits and English letters (lower-case and/or upper-case),
+ */
+
+/**
+ * @param {string} s
+ * @return {string}
+ */
+var longestPalindrome = function (s) {
+  var max = 0;
+  var head = 0;
+  var n = s.length;
+  var i = 0;
+  while (i < n - max / 2) {
+    var lo = i;
+    while (i < n && s[i] === s[lo]) {
+      i++;
+    }
+    var hi = i - 1;
+    while (lo >= 0 && hi < n && s[lo] === s[hi]) {
+      lo--;
+      hi++;
+    }
+    if (hi - lo - 1 > max) {
+      max = hi - lo - 1;
+      head = lo + 1;
+    }
+  }
+  return s.slice(head, head + max);
+};

README.md

@@ -220,6 +220,8 @@ Check out ---> [Sample PR](https://github.com/codedecks-in/LeetCode-Solutions/pu
 | --- | --------------------------------------------------------------------------------------------- | --------------------------------------------------- | -------- | ------ | ---------- | --- | ---------------- |
 | 005 | [Longest Palindromic Substring](https://leetcode.com/problems/longest-palindromic-substring/) | [Python](./Python/5_LongestPalindromicSubstring.py) | _O(N^2)_ | _O(N)_ | Medium     |     | Expand the Wings |
 | 4   | [Median of Two Sorted Arrays](https://leetcode.com/problems/median-of-two-sorted-arrays/)     | [Java](./Java/median-of-two-sorted-arrays.java)    | _O(log(min(m,n)))_ | _O(1)_ | Hard |  |  |
+| 005   | [Longest Palindromic Substring](https://leetcode.com/problems/longest-palindromic-substring/)     | [JavaScript](./JavaScript/5.Longest-Palindromic-Substring.js)    | _O(N^2)_ | _O(1)_ | Medium |  |  |
+
 <br/>
 <div align="right">
     <b><a href="#algorithms">⬆️ Back to Top</a></b>