advent of code, day 15, part b

adventOfCode15b.scala

// See problem on Advent of Code 
// http://adventofcode.com/2017/day/15

import annotation.tailrec

object adventOfCode15 {
  // generic testmethod 
  def test [I, O] (indata: I, outdata: O, f: (I => O)) : Boolean = {
    val res = f(indata)
    if (res == outdata) {
      println ("Success: " + indata.toString ().take (200) + "\t" + res)
      true  
    }
    else {
      println ("--Fail: f(" + indata.toString ().take (200) + ")\t= " + res + "\texpected: " + outdata)
      false    
    }
  }  
  
  case class Tor15b (startvalA: Long, startvalB: Long) {
    val m = Int.MaxValue
    val m5 = 5*1000*1000

    def lowbits (i: Long) : Long = ((i << 48) >> 48) 

    // count downwards from 5M steps, stop at 0
    @tailrec 
    final def addMatches (steps: Int, sum: Int, a: Long, b: Long) : Int = steps match {
      case 0  => sum
      case _  => {
          val aval : Long = a * 16807 % m 
          val bval : Long = b * 48271 % m 
          // if (aval == 1023762912L) println (s"---> aVal found! step: ${1+m5-steps} a: $aval b: $bval")
          
          if ((aval & 3L) == 0L && (bval & 7L) == 0L) {
            val hit = if (lowbits(a)==lowbits(b)) 1 else 0
            if (hit == 1) println (s"hit: step ${1+m5-steps} a: $aval b: $bval")
            addMatches (steps - 1, sum + hit, aval, bval)      
          }
          // proceede with previous values (a or b) for the one, who found divisibility:
          else if ((aval & 3) == 0) addMatches (steps, sum, a, bval)
          else if ((bval & 7) == 0) addMatches (steps, sum, aval, b)
          else addMatches (steps, sum, aval, bval)
      }
    }
    
    // ein off-by-one-Error?
    def findMatches (anz: Int) = addMatches (anz+1, 0, startvalA, startvalB)     
  }
  
  // fill program with test- and serious values
  def tor15btest () : Boolean = {
    val m5 = 1000*1000*5
    // testdata:
    val tor15bt = Tor15b (65L, 8921L)	

    test (1055, 0, tor15bt.findMatches)
    println ("---------------------")
    test (1056, 1, tor15bt.findMatches)
    println ("---------------------")
    test (1057, 1, tor15bt.findMatches)
    println ("---------------------")
    test (m5, 309, tor15bt.findMatches) // fail 69 => echo $(((5*67+4*(67-1)+1)/2)) = 309 => 67 statt 69: => 300
    // serious data:
    //Generator A starts with 618,  B starts with 814
    val tor15bp = Tor15b (618L, 814L)	
    // 999 is just a dummy value, to satisfy the test syntax
    test (m5, 999, tor15bp.findMatches) // findet 67 => 300 too low, 302 too low
  }

  def main (s: Array[String]) : Unit = tor15btest 
}