Added longestPalindromic solution

Author: nhistory

longest-palindromic-substring/nhistory.js

@@ -0,0 +1,32 @@
+var longestPalindrome = function (s) {
+  let maxStart = 0,
+    maxEnd = 0;
+
+  for (let i = 0; i < s.length; i++) {
+    let start = i,
+      end = i;
+    while (start >= 0 && end < s.length && s[start] === s[end]) {
+      if (end - start > maxEnd - maxStart) {
+        maxStart = start;
+        maxEnd = end;
+      }
+      start--;
+      end++;
+    }
+
+    (start = i), (end = i + 1);
+    while (start >= 0 && end < s.length && s[start] === s[end]) {
+      if (end - start > maxEnd - maxStart) {
+        maxStart = start;
+        maxEnd = end;
+      }
+      start--;
+      end++;
+    }
+  }
+
+  return s.slice(maxStart, maxEnd + 1);
+};
+
+// TC: O(n^2)
+// SC: O(1)