Starting to get a little tough. I managed to get this after examining some of the solutions posted here. I had a naive solution for part 1 that was off by one and I can’t figure out why. Since my final solution was derivative of other posts here not posting it but wanted to say thanks for everyone who did post their solutions for providing the guidance.
stevensonmt
jarimatti
That’s a nice implementation of count_bags/2, much more readable than what I managed to do.
0
jarimatti
I modeled the data as directed graph where the edge label is the count of bags inside the source bag using Erlang :digraph and :digraph_utils. Part 2 turned out with similar (not tail-recursive) structure. Not the most elegant but gets the job done:
def count_bags_from(graph, node) do
edges =
for e <- :digraph.out_edges(graph, node) do
:digraph.edge(graph, e)
end
own_counts =
edges
|> Enum.map(fn {_e, _from, _to, count} -> count end)
|> Enum.sum()
counts =
for {_e, _from, to, count} <- edges do
count * count_bags_from(graph, to)
end
own_counts + Enum.sum(counts)
end
The benefit of :digraph is in the solution for first part:
def part1 do
graph = read_input()
result = length(Digraph.reaching(graph, "shiny gold"))
Digraph.delete(graph)
result
end
where Digraph.reaching/2 is defined as:
defmodule AoC2020.Day7.Digraph do
...
def reaching(g, target) do
:digraph_utils.reaching([target], g) -- [target]
end
...
end
0
adamu
stevensonmt
I was one short. I think on the final match I was returning before adding it to the stack, but not sure.
0
adolfont
I am not doing it every day, so only today I solved Day 7.
Ugly code, I believe.
https://github.com/Introduction-to-Functional-Programming/simple_exercises/blob/main/adolfont/adventofcode/2020/day_07/lib/day07.ex
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