Optimize gaussian elimination solution evaluation

Author: sim642

src/main/scala/eu/sim642/adventofcodelib/GaussianElimination.scala

@@ -10,14 +10,24 @@ object GaussianElimination {
  case class Solution[A: Integral](dependentVars: Seq[Int], dependentGenerator: Seq[A],
  freeVars: Seq[Int], freeGenerators: Seq[Seq[A]],
  const: Seq[A]) {
+ private lazy val freeGeneratorsTransposed = { // transpose of empty generators needs right length for lazyZip to work below
+ if (freeGenerators.isEmpty)
+ const.map(_ => Nil)
+ else
+ freeGenerators.transpose
+ }
+
+ require(dependentGenerator.size == const.size)
+ require(dependentGenerator.size == freeGeneratorsTransposed.size)
+
  def evaluate(freeVals: Seq[A]): Seq[A] = {
- (dependentGenerator lazyZip const).zipWithIndex.map({case ((mainVar, v), i) =>
- val r = v - (freeGenerators lazyZip freeVals).map((freeVar, freeVal) => freeVar(i) * freeVal).sum
+ (const lazyZip freeGeneratorsTransposed lazyZip dependentGenerator).map((v, fgt, mainVar) => {
+ val r = v - (fgt lazyZip freeVals).map(_ * _).sum
  if (r % mainVar == 0)
  r / mainVar
  else
  -summon[Integral[A]].one // TODO: Option
- }).toList
+ })
  }
  }
 
@@ -101,8 +111,8 @@ object GaussianElimination {
  dependentVars = mainVars.toSeq,
  dependentGenerator = (mainVars lazyZip m).view.map((v, row) => row(v)).toSeq,
  freeVars = freeVars.toSeq,
- freeGenerators = freeVars.view.map(x => m.view.map(_(x)).toSeq).toSeq,
- const = m.view.map(_.last).toSeq
+ freeGenerators = freeVars.view.map(x => m.view.take(mainVars.size).map(_(x)).toSeq).toSeq,
+ const = m.view.take(mainVars.size).map(_.last).toSeq
  )
  }
 }