Valid Palindrome (easy)

class Solution {
  public boolean isPalindrome(String s) {
    // TODO: Write your code here
    s = s.toLowerCase();
    int st = 0;
    s = s.toLowerCase();
    int ed = s.length() - 1;
    char[] curS = s.toCharArray();

    while (st < ed) {
      char curSt = curS[st];
      char curEd = curS[ed];

      if (curSt > 'a' && curSt < 'z' && curEd > 'a' && curEd < 'z') {
        if (curSt != curEd) return false;
        st++;
        ed--;
      } else if (curSt > 'a' && curSt < 'z') {
        ed--;
      } else if (curEd > 'a' && curEd < 'z') {
        st++;
      } else {
        st++;
        ed--;
      }
    }
    return true; 
  }
}

class Solution:
  def isPalindrome(self, s: str) -> bool:
    # TODO: Write your code here
    str_array = []
    for char in s:
      if char.isalpha() or char.isdigit():
        str_array.append(char.lower())
    front, back = 0, len(str_array) - 1
    while front < back:
      if str_array[front] != str_array[back]:
        return False
      front += 1
      back -= 1
    return True