Advent of Code F# – Day 23

The source code for this post (both Part 1 and Part 2) is available here and you can click here to see my solutions for the other Advent of Code challenges.

Description for today’s challenge is here.


First, let’s define the 6 instructions on the computer:


and parse the input file (see example below) into the DU type above

jio a, +16

inc a

tpl a

inc a

jmp +23


Then we add a function to iterate through the instructions, a simple (tail) recursive loop function would do the trick. The below should be pretty self-explanatory, two tricky things to keep in mind:

  • that jio stood for “jump if one” rather than the more intuitive “jump if odd” given that jie is “jump if even”…
  • the problem specifies the register value to be non-negative, and just in case we’ll overflow, use an unsigned long


and all that’s left is to call the function with the instructions we have parsed from the input and ask for the value of the b register at the end.



Part 2

For Part 2, we just need to change the initial register values we pass into the loop:


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  1. Pingback: F# Weekly #52, 2015-IT??

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