# ScalaEuler / src / com / mklinke / euler / Problem37.scala

 ``` 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78``` ```/** * * * Copyright 2012 Martin Klinke, http://www.martinklinke.com. * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package com.mklinke.euler /** * @author Martin Klinke * */ object Problem37 { def main(args: Array[String]) { val start = System.currentTimeMillis; println("Sum of truncatable primes: " + sumTruncatablePrimes(10, 0, 0)) println("Duration: " + (System.currentTimeMillis - start) + " ms"); } def sumTruncatablePrimes(currentN: Int, count: Int, currentSum: Int): Int = { if (count == 11) currentSum else { val foundMatch = isTruncatablePrime(currentN) sumTruncatablePrimes(currentN + 1, if (foundMatch) count + 1 else count, if (foundMatch) currentSum + currentN else currentSum) } } def isTruncatablePrime(n: Int): Boolean = { isLeftTruncatablePrime(n) && isRightTruncatablePrime(n) } def isLeftTruncatablePrime(n: Int): Boolean = { val digits = n.toString.toList if (digits.length == 1) isPrime(digits.head - 48) else isPrime(n) && isLeftTruncatablePrime(digits.tail.map(c => c - 48).mkString.toInt) } def isRightTruncatablePrime(n: Int): Boolean = { val digits = n.toString.toList if (digits.length == 1) isPrime(digits.head - 48) else isPrime(n) && isRightTruncatablePrime(digits.reverse.tail.reverse.map(c => c - 48).mkString.toInt) } def isPrime(n: Int): Boolean = { if (n == 1) false else n == smallestDivisor(n) } def smallestDivisor(n: Int): Int = { findDivisor(n, 2) } def findDivisor(n: Int, testDivisor: Int): Int = { if (testDivisor * testDivisor > n) n else if (n % testDivisor == 0) testDivisor else findDivisor(n, testDivisor + 1) } } ```