[Day 14] Precompute positions of cube-shaped rocks

README.md

@@ -23,7 +23,7 @@ This Julia package contains my solutions for [Advent of Code 2023](https://adven
 | 11 | [:white_check_mark:](https://adventofcode.com/2023/day/11) | 4.728 ms | 1.71 MiB | [:white_check_mark:](https://github.com/goggle/AdventOfCode2023.jl/blob/master/src/day11.jl) |
 | 12 | [:white_check_mark:](https://adventofcode.com/2023/day/12) | 9.320 ms | 2.64 MiB | [:white_check_mark:](https://github.com/goggle/AdventOfCode2023.jl/blob/master/src/day12.jl) |
 | 13 | [:white_check_mark:](https://adventofcode.com/2023/day/13) | 2.202 ms | 3.18 MiB | [:white_check_mark:](https://github.com/goggle/AdventOfCode2023.jl/blob/master/src/day13.jl) |
-| 14 | [:white_check_mark:](https://adventofcode.com/2023/day/14) | 72.359 ms | 62.11 MiB | [:white_check_mark:](https://github.com/goggle/AdventOfCode2023.jl/blob/master/src/day14.jl) |
+| 14 | [:white_check_mark:](https://adventofcode.com/2023/day/14) | 36.220 ms | 28.00 MiB | [:white_check_mark:](https://github.com/goggle/AdventOfCode2023.jl/blob/master/src/day14.jl) |
 | 15 | [:white_check_mark:](https://adventofcode.com/2023/day/15) | 2.647 ms | 1.49 MiB | [:white_check_mark:](https://github.com/goggle/AdventOfCode2023.jl/blob/master/src/day15.jl) |
 | 16 | [:white_check_mark:](https://adventofcode.com/2023/day/16) | 65.902 ms | 53.79 MiB | [:white_check_mark:](https://github.com/goggle/AdventOfCode2023.jl/blob/master/src/day16.jl) |
 | 17 | [:white_check_mark:](https://adventofcode.com/2023/day/17) | 5.126 s | 467.29 MiB | [:white_check_mark:](https://github.com/goggle/AdventOfCode2023.jl/blob/master/src/day17.jl) |

src/day14.jl

@@ -4,23 +4,38 @@ using AdventOfCode2023
 
 function day14(input::String = readInput(joinpath(@__DIR__, "..", "data", "day14.txt")))
     data = map(x -> x[1], reduce(vcat, permutedims.(map(x -> split(x, ""), split(input)))))
-    return [part1(data), part2(data)]
+
+    # Precompute the positions of the cube-shaped rockes, so that it must
+    # not be done in every tilting step again.
+    cubepos = Dict{Int,Dict{Int, Vector{Int}}}()
+    mat = data
+    for i = 0:3
+        cubepos[i] = Dict{Int,Vector{Int}}()
+        for (j, col) ∈ enumerate(eachcol(mat))
+            cubes = findall(x -> x == '#', col)
+            pushfirst!(cubes, 0)
+            push!(cubes, length(col) + 1)
+            cubepos[i][j] = cubes
+            mat = rotr90(mat)
+        end
+    end
+    return [part1(data, cubepos), part2(data, cubepos)]
 end
 
-function part1(data::Matrix{Char})
+function part1(data::Matrix{Char}, cubepos::Dict{Int,Dict{Int, Vector{Int}}})
     d = copy(data)
-    tilt_north!(d)
+    tilt_north!(d, 0, cubepos)
     return score(d)
 end
 
-function part2(data::Matrix{Char})
+function part2(data::Matrix{Char}, cubepos::Dict{Int,Dict{Int, Vector{Int}}})
     mat = copy(data)
 
     d = Dict{String,Int}()
     d[join(mat)] = 0
     first = last = 0
     for n ∈ 1:1_000_000_000
-        mat = cycle!(mat)
+        mat = cycle!(mat, cubepos)
         s = join(mat)
         if haskey(d, s)
             first = d[s]
@@ -31,16 +46,14 @@ function part2(data::Matrix{Char})
     end
     steps_left = mod(10^9 - last, last - first)
     for _ ∈ 1:steps_left
-        mat = cycle!(mat)
+        mat = cycle!(mat, cubepos)
     end
     return score(mat)
 end
 
-function tilt_north!(mat::Matrix{Char})
-    for col ∈ eachcol(mat)
-        cubes = findall(x -> x == '#', col)
-        pushfirst!(cubes, 0)
-        push!(cubes, length(col) + 1)
+function tilt_north!(mat::Matrix{Char}, orientation::Int, cubepos::Dict{Int,Dict{Int, Vector{Int}}})
+    for (j, col) ∈ enumerate(eachcol(mat))
+        cubes = cubepos[orientation][j]
         for i ∈ firstindex(cubes):lastindex(cubes)-1
             c1, c2 = cubes[i], cubes[i+1]
             c2 - c1 == 1 && continue
@@ -61,9 +74,9 @@ function score(mat::Matrix{Char})
     return s
 end
 
-function cycle!(mat::Matrix{Char})
-    for _ ∈ 1:4
-        tilt_north!(mat)
+function cycle!(mat::Matrix{Char}, cubepos::Dict{Int,Dict{Int, Vector{Int}}})
+    for i ∈ 0:3
+        tilt_north!(mat, i, cubepos)
         mat = rotr90(mat)
     end
     return mat