func (sol *Solution) isPalindrome(s string) bool {
    first, last := 0, len(s) - 1

    for first < last {
        r1, r2 := rune(s[first]), rune(s[last])

        if !unicode.IsLetter(r1) && !unicode.IsDigit(r1) {
            first++
            continue
        }

        if !unicode.IsLetter(r2) && !unicode.IsDigit(r2) {
            last--
            continue
        }

        if unicode.ToLower(r1) != unicode.ToLower(r2) {
            return false
        }

        first++
        last--
    }

    return true
}

Pretty similar to the original solution, but the conditional expressions with continue as opposed to the inner for loops feels a bit easier for me to follow.