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class Solution {
    fun isPalindrome(s: String): Boolean {

        var start = 0
        var end = s.length - 1

        while(start < end) {
            var f = s[start]
            var b = s[end]

            when{
                !f.isLetterOrDigit() -> start++
                !b.isLetterOrDigit() -> end--
                f.lowercaseChar() != b.lowercaseChar() -> return false
                else -> {start++; end--}
            }
        }
        return true
    }
}