Update 125. Valid Palindrome.md

Author: ps0305

101-200/125. Valid Palindrome.md

@@ -61,3 +61,34 @@ nope.
 
 * Time complexity : O(n).
 * Space complexity : O(n).
+
+
+```js
+/**
+ * @param {string} s
+ * @return {boolean}
+ */
+var isPalindrome = function(s) {
+    
+    s = s.toLowerCase().replace(/[\W_]/g, '');
+    
+    let left = 0;
+    let right = s.length - 1;
+    
+    while (left < right) {
+        if (s[left] !== s[right])  {
+            return false
+        }
+        left++;
+        right--;
+    }
+    
+    return true;
+    
+};
+```
+
+**Complexity:**
+
+* Time complexity : O(n).
+* Space complexity : O(1). left and right pointers take the constant space.