advent_of_code_2022

commit 5e7795bf910a8778d153bad8fa4e6f00fc72e1c9
parent 5cb1d122c0f1f461fe36828fc2f003e5373eafa4
Author: Eamon Caddigan <eamon.caddigan@gmail.com>
Date:   Mon,  5 Dec 2022 16:28:23 -0800

Solution to day 5, part 2.

Diffstat:
M
src/day_5.jl
 | 
31
++++++++++++++++++++++++++++++-

1 file changed, 30 insertions(+), 1 deletion(-)
diff --git a/src/day_5.jl b/src/day_5.jl
@@ -68,7 +68,36 @@ end
 @assert part_1(example) == "CMZ"
 @info part_1(input)
 
+## Part 2
+
+# Need a new function for applying instructions. Wish I was smarter about Julia
+# polymorphism, but whatever.
+
+# Apply an instruction to the crate stacks. Does nothing with invalid
+# instructions (doesn't throw warnings or errors either).
+function apply_instruction_2!(stacks, instruction)
+    m = match(r"move (\d+) from (\d+) to (\d+)", instruction)
+    if !isnothing(m)
+        (numtomove, from, to) = parse.(Int, m.captures)
+        push!(stacks[to], stacks[from][end-numtomove+1:end]...)
+        deleteat!(stacks[from],
+                  lastindex(stacks[from])-numtomove+1:lastindex(stacks[from]))
+    end
+    stacks
+end
+
+# Apply all the instructions to the crate stacks
+function apply_all_instructions_2!(stacks, instructions)
+    for instruction = instructions
+        apply_instruction_2!(stacks, instruction)
+    end
+    stacks
+end
+
 function part_2(input)
-    nothing
+    (cratestack, instructions) = split_input(input)
+    stacks = apply_all_instructions_2!(parse_stack(cratestack), instructions)
+    reduce(*, last.(stacks))
 end
+@assert part_2(example) == "MCD"
 @info part_2(input)