day_7

The central idea of this is to represent each possible combination of n operators with an n-ary number.

So for part 1, which only uses two operators, we can use a binary number:

1011 would represent the combination of a + b * c + d + e

Part 2 uses three operators, so we can use a ternary number:

102 would represent the combination of a + b * c <concat> d

This way, we can range over all possible combinations of operators and apply them to the input.

Enumerating all possibilities isn’t the most efficient way, but the get_operator_combination function is rather elegant.

pub fn get_operator_combinations(
  input: List(Int),
  num_operators: Int,
) -> List(List(fn(Int, Int) -> Int))

pub fn main() -> Nil

pub fn parse_row(row: String) -> #(Int, List(Int))

pub fn part_1() -> Int

pub fn part_2() -> Int