RotatePerformance.kt

import java.util.*
import kotlin.system.measureTimeMillis

fun main(args: Array<String>) {
    val nTests = 20000
    val testLength = 10000

    val random = Random()

    val strs = (1..nTests).map { (1..testLength).map { (random.nextInt() % 10) }.joinToString() }

    val dropTakeTime = measureTimeMillis { strs.forEach { it.drop(1) + it.first() } }
    val arrayTime = measureTimeMillis {
        strs.forEach { str ->
            str.toCharArray().let { it ->
                for (i in 0..it.lastIndex - 1)
                    it[i] = it[i + 1]
                it[it.lastIndex] = str[0] // str is unchanged
                String(it)
            }
        }
    }
    val builderTime = measureTimeMillis {
        strs.forEach { str ->
            var builder = StringBuilder()
            for (i in 0..str.length - 2) {
                builder.append(str[i+1])
            }
            builder.append(str[0])
            builder.toString()
        }
    }

    println("drop + take: $dropTakeTime ms")
    println("array: $arrayTime ms")
    println("builder: $builderTime ms")
}

// drop + take: 1076 ms
// array: 1038 ms
// builder: 4435 ms