Finished 2020 day 13

2020/data/day_13.txt

@@ -0,0 +1,2 @@
+1008832
+23,x,x,x,x,x,x,x,x,x,x,x,x,41,x,x,x,x,x,x,x,x,x,449,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,13,19,x,x,x,x,x,x,x,x,x,29,x,991,x,x,x,x,x,37,x,x,x,x,x,x,x,x,x,x,17

2020/src/day_12.jl

@@ -11,8 +11,7 @@ function step_ship(inst, pos, dir, part_2=false)
         pos += val*dir
     elseif comm == 'R' || comm == 'L'
         s,c = map(x->Int(round(x(deg2rad(val)))), [sin, cos])
-        dir *= comm == 'R' ? [c -s; s c] :
-                             [c s; -s c]
+        dir *= comm == 'R' ? [c -s; s c] : [c s; -s c]
     elseif !part_2
         pos += val*dirs[comm]
     else

2020/src/day_13.jl

@@ -0,0 +1,19 @@
+# https://adventofcode.com/2020/day/13
+using AdventOfCode
+using Mods
+
+t_str, buses_str = readlines("2020/data/day_13.txt")
+time = parse(Int, t_str)
+buses = map(x->x=="x" ? nothing : parse(Int, x), split(buses_str, ','))
+
+function part_1()
+    wait, bus = min(map(x->(x*ceil(time / x), x), filter(!isnothing, buses))...)
+    (wait - time) * bus
+end
+@info part_1()
+
+function part_2()
+    mods = map(k->Mod{buses[k]}(-(k-1)), filter(k->!isnothing(buses[k]), keys(buses)))
+    CRT(mods...).val
+end
+@info part_2()

Project.toml

@@ -2,3 +2,4 @@
 AdventOfCode = "7ef4cfdd-3fec-4d8b-b242-bcc5161d01d5"
 Combinatorics = "861a8166-3701-5b0c-9a16-15d98fcdc6aa"
 MD5 = "6ac74813-4b46-53a4-afec-0b5dc9d7885c"
+Mods = "7475f97c-0381-53b1-977b-4c60186c8d62"