Day 7
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defmodule Day7 do
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def get_requirement(str) do
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[_, requirement, step] = Regex.run(~r/Step (\w) must be finished before step (\w) can begin./, str)
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{step, requirement}
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end
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def all_nodes(requirements) do
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requirements
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|> Enum.reduce([], fn {step, req}, acc ->
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[step | [req | acc]]
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end)
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|> Enum.uniq
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end
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def create_graph(requirements) do
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Enum.reduce(requirements, %{}, fn {step, req}, acc ->
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Map.update(acc, step, [req], &([req | &1]))
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end)
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end
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@doc """
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Topological sort implemented using Kahn's algorithm: https://en.wikipedia.org/wiki/Topological_sorting#Kahn's_algorithm
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"""
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def kahn(_nodes, sorted, _graph, []), do: Enum.reverse(sorted)
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def kahn(nodes, sorted, graph, no_incoming_edges) do
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# sort no_incoming_edges lexicographically as per AoC problem
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[n | rest_no_incoming_edges] = no_incoming_edges |> Enum.sort()
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sorted = [n | sorted]
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{graph, no_incoming_edges} =
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nodes
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|> Enum.filter(fn m -> n in Map.get(graph, m, []) end)
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|> Enum.reduce({graph, rest_no_incoming_edges}, fn m, {graph, no_incoming_edges} ->
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new_dependencies_of_m = graph |> Map.get(m) |> List.delete(n)
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new_graph = graph |> Map.put(m, new_dependencies_of_m)
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{
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new_graph,
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case new_dependencies_of_m do
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[] -> [m | no_incoming_edges]
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_ -> no_incoming_edges
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end
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}
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end)
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kahn(nodes, sorted, graph, no_incoming_edges)
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end
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def kahn(nodes, graph) do
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no_incoming_edges = Enum.filter(nodes, fn node -> !Map.has_key?(graph, node) end)
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kahn(nodes, [], graph, no_incoming_edges)
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end
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def step_time(nil), do: 0
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def step_time(<<c::utf8, _rest::binary>>) do
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# step - ?A + 1 + extra
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c - ?A + 60
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end
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def tick(workers, nodes, graph, done \\ [], time \\ 0) do
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{workers, {done, nodes}} =
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Enum.map_reduce(workers, {done, nodes}, fn {current_step, remaining}, {done, nodes} ->
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case remaining do
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0 ->
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new_done = case current_step do
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nil -> done
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_ -> [current_step | done]
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end
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next_step =
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nodes
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|> Enum.find(fn node ->
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Enum.all?(Map.get(graph, node, []), fn dep -> dep in new_done end)
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end)
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new_nodes = List.delete(nodes, next_step)
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{{next_step, step_time(next_step)}, {new_done, new_nodes}}
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n when n > 0 ->
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{{current_step, n - 1}, {done, nodes}}
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end
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end)
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IO.inspect(nodes)
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IO.inspect(done)
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IO.inspect(workers)
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if length(nodes) == 0 and Enum.all?(workers, fn {step, _} -> step == nil end) do
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time - 1
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else
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tick(workers, nodes, graph, done, time + 1)
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end
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end
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def parse_input() do
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File.read!("lib/day7/input.txt")
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|> String.split("\n", trim: true)
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|> Enum.map(&get_requirement/1)
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end
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def part1() do
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requirements = parse_input()
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nodes = all_nodes(requirements)
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graph = create_graph(requirements)
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kahn(nodes, graph)
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|> Enum.join()
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end
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def part2() do
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requirements = parse_input()
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nodes = all_nodes(requirements)
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graph = create_graph(requirements)
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workers = for _ <- 1..5, do: {nil, 1}
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tick(workers, nodes, graph)
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end
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end
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@ -0,0 +1,101 @@
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Step T must be finished before step C can begin.
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Step V must be finished before step C can begin.
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Step Y must be finished before step H can begin.
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Step R must be finished before step U can begin.
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Step B must be finished before step J can begin.
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Step Q must be finished before step O can begin.
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Step W must be finished before step O can begin.
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Step S must be finished before step X can begin.
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Step I must be finished before step N can begin.
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Step X must be finished before step H can begin.
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Step M must be finished before step L can begin.
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Step A must be finished before step F can begin.
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Step G must be finished before step P can begin.
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Step U must be finished before step E can begin.
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Step Z must be finished before step E can begin.
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Step H must be finished before step L can begin.
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Step P must be finished before step C can begin.
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Step K must be finished before step F can begin.
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Step O must be finished before step C can begin.
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Step C must be finished before step F can begin.
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Step D must be finished before step L can begin.
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Step L must be finished before step F can begin.
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Step N must be finished before step E can begin.
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Step J must be finished before step F can begin.
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Step F must be finished before step E can begin.
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Step I must be finished before step A can begin.
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Step Z must be finished before step J can begin.
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Step I must be finished before step P can begin.
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Step T must be finished before step E can begin.
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Step R must be finished before step F can begin.
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Step U must be finished before step H can begin.
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Step K must be finished before step E can begin.
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Step D must be finished before step N can begin.
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Step U must be finished before step C can begin.
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Step D must be finished before step J can begin.
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Step N must be finished before step F can begin.
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Step C must be finished before step J can begin.
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Step U must be finished before step J can begin.
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Step A must be finished before step O can begin.
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Step H must be finished before step N can begin.
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Step P must be finished before step O can begin.
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Step I must be finished before step E can begin.
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Step G must be finished before step F can begin.
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Step O must be finished before step J can begin.
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Step Q must be finished before step F can begin.
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Step G must be finished before step J can begin.
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Step X must be finished before step E can begin.
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Step S must be finished before step D can begin.
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Step R must be finished before step P can begin.
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Step K must be finished before step L can begin.
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Step R must be finished before step Q can begin.
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Step L must be finished before step N can begin.
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Step Q must be finished before step C can begin.
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Step C must be finished before step D can begin.
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Step C must be finished before step N can begin.
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Step O must be finished before step E can begin.
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Step W must be finished before step F can begin.
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Step K must be finished before step D can begin.
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Step T must be finished before step H can begin.
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Step M must be finished before step D can begin.
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Step Y must be finished before step Z can begin.
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Step J must be finished before step E can begin.
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Step S must be finished before step F can begin.
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Step G must be finished before step U can begin.
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Step V must be finished before step S can begin.
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Step Y must be finished before step F can begin.
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Step G must be finished before step H can begin.
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Step T must be finished before step Q can begin.
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Step S must be finished before step U can begin.
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Step V must be finished before step D can begin.
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Step W must be finished before step M can begin.
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Step M must be finished before step E can begin.
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Step A must be finished before step H can begin.
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Step B must be finished before step F can begin.
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Step B must be finished before step N can begin.
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Step D must be finished before step F can begin.
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Step W must be finished before step K can begin.
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Step P must be finished before step E can begin.
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Step B must be finished before step X can begin.
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Step Q must be finished before step U can begin.
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Step Q must be finished before step X can begin.
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Step X must be finished before step N can begin.
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Step M must be finished before step Z can begin.
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Step G must be finished before step Z can begin.
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Step S must be finished before step G can begin.
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Step P must be finished before step F can begin.
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Step I must be finished before step O can begin.
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Step R must be finished before step A can begin.
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Step L must be finished before step J can begin.
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Step B must be finished before step I can begin.
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Step C must be finished before step E can begin.
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Step B must be finished before step W can begin.
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Step P must be finished before step N can begin.
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Step H must be finished before step C can begin.
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Step K must be finished before step J can begin.
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Step Y must be finished before step M can begin.
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Step Z must be finished before step P can begin.
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Step I must be finished before step K can begin.
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Step V must be finished before step E can begin.
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Step Y must be finished before step P can begin.
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Step T must be finished before step R can begin.
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@ -0,0 +1,4 @@
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defmodule Day7Test do
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use ExUnit.Case
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doctest Day7
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end
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