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DavidM_

Not the most elegant, but we got there: https://gist.github.com/dmckennell/45bc2e70e2990e43e262ffbcee95f67f

Couldn't avoid running the program a second time in part 2 when I discover the program is completing successfully following a swap. Would like to have memoized the program result used in my if condition, but not seeing an easy way to manage that with collectFirst.

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wence in reply to @DavidM_

Not really au-fait with Scala but I would have thought you could pattern-match on the result of swapAndExecute? Almost certainly not correct syntax, but something like

    input.zipWithIndex.collectFirst {
      case (instruction, index) 
         swapAndExecute(input, instruction, index) match {
           case LoopResult(acc, Completed) => acc,
           case other => None,
      }
}.get

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DavidM_ in reply to @wence

Sadly no - collectFirst takes a partial function (in this case PartialFunction[(Instruction, Int), Int]) which I can't wrangle the input collection into. It's a bit of a 'square peg round hole' situation. I should probably craft something myself for such a case.

In your code snippet the case would be satisfied on the first instruction and I would then get a NoSuchElementException.

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