Merge pull request #2535 from acidbluebriggs/patch-1

Author: aakhtar3

javascript/0125-valid-palindrome.js

@@ -55,3 +55,33 @@ var isPalindrome = function(s) {
     }
     return true;
 };
+
+/**
+ * 2 Pointer | Midde Convergence | No RegEx | No Copying
+ * Time O(N) | Space O(1)
+ * https://leetcode.com/problems/valid-palindrome/
+ * @param {string} s
+ * @return {boolean}
+ */
+var isPalindrome = function (s) {
+  const isAlphaNumeric = c => (c.toLowerCase() >= 'a' && c.toLowerCase() <= 'z') || c >= '0' && c <= '9'
+
+  let left = 0;
+  let right = s.length - 1;
+  let skipLeft, skipRight, endsEqual = false;
+  
+  while (left < right) {
+    skipLeft = !isAlphaNumeric(s.charAt(left))
+    if (skipLeft) { left++; continue; }
+
+    skipRight = !isAlphaNumeric(s.charAt(right))
+    if (skipRight) { right--; continue; }
+
+    endsEqual = s.charAt(left).toLowerCase() === s.charAt(right).toLowerCase()
+    if (!endsEqual) return false
+
+    left++
+    right--
+  }
+  return true
+};