Valid Palindrome

Problem Statement

Given a string, determine if it is a palindrome, considering only alphanumeric characters and ignoring cases.

Example:

"A man, a plan, a canal: Panama" is a palindrome.
"race a car" is not a palindrome.

Note:

Have you consider that the string might be empty? This is a good question to ask during an interview.

For the purpose of this problem, we define empty string as valid palindrome.

Solution

Link to GitHub python:Code

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def isPalindrome(s): head,tail=0,len(s)-1 while head < tail: while head <tail and not s[head].isalnum(): head+=1 while head <tail and not s[tail].isalnum(): tail-=1 if s[head].lower() != s[tail].lower(): return False head+=1; tail-=1 return True isPalindrome("bob bob")

Link to GitHub Java  :Code
Link to GitHub JavaScript:  Code

• We need 2 pointers head and tail
• Head is the initial position and tail is the last position in the array
• Increment the header if we do not find valid character .Decrement the tail if we do not find the valid character.
• Loop through the array till we find tail is greater than head
• Return false if header character is not equal to tail

public static boolean get(String str)
 {
  //if string is empty return true
  if(str.isEmpty())
  {
   return true;
  }
  int head =0, tail=str.length()-1;
  //loop  through the strings to find if it is a valid palindrome
   while(head <= tail)
   {
    //Increment the header if the character isLetter or digit
    if(!Character.isLetterOrDigit(str.charAt(head))){
     head++;
    }
    //Decrement the tail if the character isLetter or digit
    else if(!Character.isLetterOrDigit(str.charAt(tail))){
     tail--;
    }
    else {
       if(Character.toLowerCase(str.charAt(head)) 

                                     !=Character.toLowerCase(str.charAt(tail)))
       {
        return false;
       }
       head++;
       tail--;
     
    }
   }
  return true;
 }