문자열의 모든 순열

fun permute(str: String, l: Int, r: Int, result: MutableList<String>) {
    if (l == r) result.add(str)
    else {
        for (i in l..r) {
            val swapped = str.toCharArray().apply {
                this[l] = this[i].also { this[i] = this[l] }
            }.joinToString("")
            permute(swapped, l + 1, r, result)
        }
    }
}

fun getAllPermutations(s: String): List<String> {
    val result = mutableListOf<String>()
    permute(s, 0, s.length - 1, result)
    return result
}