Added validPalindrome solution

Author: nhistory

valid-palindrome/nhistory.js

@@ -0,0 +1,43 @@
+/**
+ * @param {string} s
+ * @return {boolean}
+ */
+var isPalindrome = function (s) {
+  // 1. Create left and right pointer
+  let l = 0;
+  let r = s.length - 1;
+  // 2. Iterate while loop with l<r condition
+  while (l < r) {
+    // 3. Check character with left pointer is alphanumeric character or not
+    if (
+      (s[l] >= "a" && s[l] <= "z") ||
+      (s[l] >= "A" && s[l] <= "Z") ||
+      (s[l] >= "0" && s[l] <= "9")
+    ) {
+      // 4. Check character with right pointer is alphanumeric character or not
+      if (
+        (s[r] >= "a" && s[r] <= "z") ||
+        (s[r] >= "A" && s[r] <= "Z") ||
+        (s[r] >= "0" && s[r] <= "9")
+      ) {
+        // 5. Compare left and right pointer character
+        if (s[l].toLowerCase() !== s[r].toLowerCase()) {
+          return false;
+        } else {
+          l++;
+          r--;
+        }
+        //    If not, go to next location for right pointer
+      } else r--;
+
+      //    If not, go to next location for left pointer
+    } else l++;
+  }
+  return true;
+};
+
+// TC: O(n)
+// SC: O(n)
+
+console.log(isPalindrome("A man, a plan, a canal: Panama")); //true
+console.log(isPalindrome("race a car")); //false