[LeetCode] 125. Valid Palindrome - kotlin

class Solution {
    fun isChar(c:Char):Boolean {
        return c.isLetter() || c.isDigit()    
    }

    fun isPalindrome(s1: String): Boolean {
        var s = 0
        var e = s1.length - 1
        var str = s1.lowercase()

        while(s<e) {
            while(!isChar(str[s])) {
                if(s+1>e) return true
                s++
            }
            while(!isChar(str[e])) {
                if(e-1<s) return true
                e--
            }

            if(str[s]!=str[e]) return false

            s++
            e--
        }

        return true
    }
}