Updated C++ Solution

Author: FarheenB

C++/soln-string-problems/valid-palindrome.cpp

@@ -10,27 +10,22 @@
 class Solution {
 public:
     bool isPalindrome(string s) {
-        transform(s.begin(),s.end(),s.begin(), ::tolower);
-        s.erase(remove(s.begin(),s.end(),' '),s.end());
         int len=s.size();
         int left=0;
         int right=len-1;
 
         while(left<right){
-            if(s[left]==s[right])
+            if(!isalnum(s[left]))
+                left++;
+            else if(!isalnum(s[right]))
+                right--;
+            else if(tolower(s[left])!=tolower(s[right]))
+                return false;
+            else
             {
                 left++;
                 right--;
-            }
-            else{
-                if((s[left]<'a' || s[left]>'z') && (s[left]<'0' || s[left]>'9'))
-                    left++;
-                else if((s[right]<'a' || s[right]>'z') && (s[right]<'0' || s[right]>'9'))
-                    right--;
-                else
-                    return false;
-            }
-                
+            }              
         }
         return true;
     }