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Contents
import java.lang.Math.max
class Series(val digits: String) {
init {
require(digits.all { it.isDigit() })
}
fun getLargestProduct(span: Int): Long {
require(span >= 0)
require(digits.length >= span)
if(digits.isEmpty()) {
return 1
}
return calculateRec(digits.map { it.intValue() }, span, 0)
}
private tailrec fun calculateRec(digits: List<Int>, span: Int, maxSoFar: Long): Long {
val currentProduct = digits.subList(0, span).prod()
val newMax = max(currentProduct, maxSoFar)
if(digits.size == span) { //since we won't be checking 'remainders' of the list, the end condition is simply when the size is the same as the span
return newMax
}
return calculateRec(digits.tail(), span, newMax)
}
}
fun Char.intValue() : Int {
if(!this.isDigit()) {
throw IllegalArgumentException("Char ${this} is not a legal DEC character")
}
return this.intDiff('0')
}
fun Char.intDiff(other: Char) = this.toInt() - other.toInt()
fun List<Int>.prod() : Long = this.fold(1L) {productSoFar, item -> item*productSoFar}
fun <T> List<T>.tail() = this.subList(1, this.size)
Version data entries
270 entries across 270 versions & 1 rubygems