// 125. Valid Palindrome

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

//

// Example 1:

//

// Input: s = "A man, a plan, a canal: Panama"

// Output: true

// Explanation: "amanaplanacanalpanama" is a palindrome.

// Example 2:

//

// Input: s = "race a car"

// Output: false

// Explanation: "raceacar" is not a palindrome.

//

//

// Constraints:

//

// 1 <= s.length <= 2 * 105

// s consists only of printable ASCII characters.

//

// Runtime: 3 ms, faster than 69.31% of Java online submissions for Valid Palindrome.

// Memory Usage: 38.8 MB, less than 81.69% of Java online submissions for Valid Palindrome.

class Solution {

public boolean isPalindrome(String s) {

s = s.toLowerCase();

int start = 0;

int end = s.length() - 1;

while (start < end) {

if (!Character.isAlphabetic(s.charAt(start)) &&

!Character.isDigit(s.charAt(start))) {

start++;

continue;

}

if (!Character.isAlphabetic(s.charAt(end))&&

!Character.isDigit(s.charAt(end))) {

end--;

continue;

}

if (s.charAt(start) == s.charAt(end)) {

start++;

end--;

} else {

return false;

}

}

return true;

}

}