/
FactorialCalculator.kt
66 lines (59 loc) 路 2.02 KB
/
FactorialCalculator.kt
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package com.lukaslechner.coroutineusecasesonandroid.usecases.coroutines.usecase12
import com.lukaslechner.coroutineusecasesonandroid.utils.addCoroutineDebugInfo
import kotlinx.coroutines.*
import timber.log.Timber
import java.math.BigInteger
class FactorialCalculator(
private val defaultDispatcher: CoroutineDispatcher = Dispatchers.Default
) {
suspend fun calculateFactorial(
factorialOf: Int,
numberOfCoroutines: Int
): BigInteger {
return withContext(defaultDispatcher) {
val subRanges = createSubRangeList(factorialOf, numberOfCoroutines)
subRanges.map { subRange ->
async {
calculateFactorialOfSubRange(subRange)
}
}.awaitAll()
.fold(BigInteger.ONE, { acc, element ->
ensureActive()
acc.multiply(element)
})
}
}
suspend fun calculateFactorialOfSubRange(
subRange: SubRange
): BigInteger {
return withContext(defaultDispatcher) {
Timber.d(addCoroutineDebugInfo("Calculate factorial of $subRange"))
var factorial = BigInteger.ONE
for (i in subRange.start..subRange.end) {
ensureActive()
factorial = factorial.multiply(BigInteger.valueOf(i.toLong()))
}
factorial
}
}
fun createSubRangeList(
factorialOf: Int,
numberOfSubRanges: Int
): List<SubRange> {
val quotient = factorialOf.div(numberOfSubRanges)
val rangesList = mutableListOf<SubRange>()
var curStartIndex = 1
repeat(numberOfSubRanges - 1) {
rangesList.add(
SubRange(
curStartIndex,
curStartIndex + (quotient - 1)
)
)
curStartIndex += quotient
}
rangesList.add(SubRange(curStartIndex, factorialOf))
return rangesList
}
}
data class SubRange(val start: Int, val end: Int)