Implement 2024 day 13 in terraform

Author: bertptrs

2024/bonus/day13/main.tf

@@ -0,0 +1,48 @@
+variable "input" {
+  type    = string
+  default = <<-EOT
+  Button A: X+94, Y+34
+  Button B: X+22, Y+67
+  Prize: X=8400, Y=5400
+  
+  Button A: X+26, Y+66
+  Button B: X+67, Y+21
+  Prize: X=12748, Y=12176
+  
+  Button A: X+17, Y+86
+  Button B: X+84, Y+37
+  Prize: X=7870, Y=6450
+  
+  Button A: X+69, Y+23
+  Button B: X+27, Y+71
+  Prize: X=18641, Y=10279
+  EOT
+}
+
+locals {
+  machines = regexall(
+    "Button A: X\\+(\\d+), Y\\+(\\d+)\nButton B: X\\+(\\d+), Y\\+(\\d+)\nPrize: X=(\\d+), Y=(\\d+)",
+    var.input
+  )
+}
+
+module "solve1" {
+  source   = "./solve"
+  machines = local.machines
+}
+
+module "solve2" {
+  source = "./solve"
+  machines = [
+    for machine in local.machines :
+    [machine[0], machine[1], machine[2], machine[3], 10000000000000 + tonumber(machine[4]), 10000000000000 + tonumber(machine[5])]
+  ]
+}
+
+output "part1" {
+  value = module.solve1.solutions
+}
+
+output "part2" {
+  value = module.solve2.solutions
+}

2024/bonus/day13/solve/main.tf

@@ -0,0 +1,34 @@
+variable "machines" {
+  type = list(list(number))
+}
+
+locals {
+  a_substitutions = [
+    for machine in var.machines :
+    [-machine[2] / machine[0], machine[4] / machine[0]]
+  ]
+
+  b_equations = [
+    for i in range(length(var.machines)) :
+    [
+      var.machines[i][3] + local.a_substitutions[i][0] * var.machines[i][1],
+      var.machines[i][5] - local.a_substitutions[i][1] * var.machines[i][1]
+    ]
+  ]
+
+  b = [for eq in local.b_equations : floor(eq[1] / eq[0] + 0.5)]
+
+  a = [
+    for i in range(length(var.machines)) :
+    floor((var.machines[i][4] - local.b[i] * var.machines[i][2]) / var.machines[i][0] + 0.5)
+  ]
+}
+
+output "solutions" {
+  value = sum([
+    for i in range(length(var.machines)) :
+    3 * local.a[i] + local.b[i]
+    if var.machines[i][0] * local.a[i] + var.machines[i][2] * local.b[i] == var.machines[i][4]
+    && var.machines[i][1] * local.a[i] + var.machines[i][3] * local.b[i] == var.machines[i][5]
+  ])
+}

2024/bonus/main.tf

@@ -79,6 +79,19 @@ output "day11_2" {
   value = module.day11.part2
 }
 
+module "day13" {
+  source = "./day13"
+  input  = file("../inputs/13.txt")
+}
+
+output "day13_1" {
+  value = module.day13.part1
+}
+
+output "day13_2" {
+  value = module.day13.part2
+}
+
 module "day19" {
   source = "./day19"
   input  = file("../inputs/19.txt")

2024/bonus/tests.tftest.hcl

@@ -148,6 +148,23 @@ run "day11" {
   }
 }
 
+run "day13" {
+  command = plan
+
+  module {
+    source = "./day13"
+  }
+
+  variables {
+    input = file("../tests/samples/13.txt")
+  }
+
+  assert {
+    condition     = output.part1 == 480
+    error_message = "Part1 output is wrong"
+  }
+}
+
 run "day19" {
   command = plan