private val charRange = ('a'..'z')

private const val limit = 1000
private const val a = 1000
private const val m = 123_987_123

fun main() {
    try {
        val firstString = "ckfiar".also { println(it) }

        val firstHash = firstString.polynomialHash(a, m)
        val sb = StringBuilder()
        generateSequence {
            val cur = sb.nextSequence().toString()//.also(::println)
            if (cur.length > limit)
                throw Error("последовательность не найдена")
            else
                cur
        }
            .first {
                it.polynomialHash(a, m) == firstHash && it != firstString
            }
            .let(::println)
    } catch (e: Throwable) {
        e.printStackTrace()
    }
}

private fun StringBuilder.nextSequence(): StringBuilder {
    if (isEmpty() || all { it == 'z' }) {
        // самое начало или все элементы -- z
        for (i in indices) this[i] = 'a'
        return append('a')
    }
    for (i in lastIndex downTo 0) {
        if (this[i] == 'z') this[i] = 'a'
        else {
            this[i] = this[i].next()
            break
        }
    }

    return this
}

private fun Char.next() = ((this.code - 96) % 26 + 97).toChar()

private fun randomString(size: Int = 20) =
    buildString {
        repeat(size) {
            append(charRange.random())
        }
    }