125. Valid Palindrome

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https://leetcode.com/problems/valid-palindrome/

String –> Two Pointers

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class Solution {
  /**
   * Character.isLetterOrDigit(char ch)
   */ 
  boolean isLetterandDigit(char ch) {
    return ch >= '0' && ch <= '9' || ch >= 'A' && ch <= 'Z' || ch >= 'a' && ch <= 'z';
  }

  boolean isPalindromeUtil(String s, int start, int end) {
    while (start < end) {
      while(!isLetterandDigit(s.charAt(start))&&start<end) start++;
      while(!isLeisLetterandDigittter(s.charAt(end))&&end>start) end--;
      if (s.charAt(start) != s.charAt(end)) return false;
      start++;
      end--;
    }
    return true;
  }

  public boolean isPalindrome(String s) {
    s = s.trim().toLowerCase();
    return isPalindromeUtil(s, 0, s.length() - 1);
  }
}

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// Regualr expression
  String removeNoneLD(String s) {
    return s.replaceAll("[^A-Za-z0-9]", "").toLowerCase();
  }
  
//   String removeNoneLD(String s) {
//     for (int i = 0; i < s.length(); i++) {
//       if (!isLetterandDigit(s.charAt(i))) {
//         s = s.substring(0, i) + s.substring(i + 1);
//         i--;
//       }
//     }
//     return s.trim().toLowerCase();
//   }

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