Added 'Valid Palindrome'

Author: anthonyzhub

Diff for: Valid Palindrome.java

@@ -0,0 +1,45 @@
+// https://leetcode.com/problems/valid-palindrome/
+
+class Solution {
+    public boolean isPalindrome(String s) {
+
+        /*
+         * Time Complexity: O(n) where n = length of string. While-loop is iterating 
+         *  string until the halfway point is reached. Keep in mind, in time and space complexity
+         *  coefficients are dropped. So, O(n) equals to O(n/2).
+         * 
+         * Space Complexity: O(1) because no additional, dynamic data structure
+         *  was created.
+         */
+        
+        // Remove all non-alphanumeric characters and them uncapitalize all letters
+        s = s.replaceAll("[^a-zA-Z0-9]", "").toLowerCase();
+
+        // If s has 1 or less characters, then it's automatically a palindrone
+        if (s.length() <= 1) {
+            return true;
+        }
+
+        // Create a left and right pointer
+        int leftPtr = 0;
+        int rightPtr = s.length() - 1;
+
+        // Iterate string
+        while (leftPtr <= rightPtr) {
+
+            // If both characters don't equal each other, return false.
+            // This string isn't a palindrone
+            if (s.charAt(leftPtr) != s.charAt(rightPtr)) {
+                return false;
+            }
+
+            // Move both pointers closer to the middle of the string
+            leftPtr += 1;
+            rightPtr -= 1;
+        }
+
+        // If function is still continuing, return true.
+        // This string is a palindrone.
+        return true;
+    }
+}