LeetCode/kt/construct-smallest-number-from-di-string.kt

class Solution {
    private fun buildSequence(
        pattern: CharArray,
        result: StringBuilder,
        index: Int,
        count: Int,
    ): Int {
        var nextCount = count
        when {
            index >= pattern.size -> {}
            pattern[index] == 'I' -> buildSequence(pattern, result, index + 1, index + 1)
            else -> {
                nextCount = buildSequence(pattern, result, index + 1, count)
            }
        }

        result.append(nextCount + 1)
        return nextCount + 1
    }

    fun smallestNumber(pattern: String): String =
        StringBuilder().let { result ->
            buildSequence(pattern.toCharArray(), result, 0, 0)

            result.reverse()
            result.toString()
        }
}