Valid Palindrome commit

src/main/java/Valid Palindrome(String)

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+--------------------------------------------------------------------------------------------------------------
+@Sayak
+Given a string, determine if it is a palindrome, considering only alphanumeric characters and ignoring cases.
+
+Note: For the purpose of this problem, we define empty string as valid palindrome.
+
+Example 1:
+
+Input: "A man, a plan, a canal: Panama"
+Output: true
+Example 2:
+
+Input: "race a car"
+Output: false
+---------------------------------------------------------------------------------------------------------------
+
+
+class Solution {
+    public boolean isPalindrome(String s) {
+
+        String fs="";
+        for(char c:s.toCharArray())
+        {
+            if(Character.isDigit(c)||Character.isLetter(c)){
+                fs+=c;
+            }
+        }
+
+        fs=fs.toLowerCase();
+        int ptr_a=0;
+        int ptr_b=fs.length()-1;
+
+        while(ptr_a<=ptr_b)
+        {
+            if(fs.charAt(ptr_a)!=fs.charAt(ptr_b)){
+                return false;
+            }
+            ptr_a++;
+            ptr_b--;
+        }
+       return true; 
+    }
+
+}