Implement day 4 in Terraform

Author: bertptrs

2024/bonus/day04/check_point/check_x_mas/main.tf

@@ -0,0 +1,30 @@
+variable "grid" {
+  type = list(string)
+}
+
+variable "x" {
+  type = number
+}
+
+variable "y" {
+  type = number
+}
+
+locals {
+  found_a = substr(var.grid[var.y], var.x, 1) == "A"
+
+  c1 = substr(var.grid[var.y - 1], var.x - 1, 1)
+  c2 = substr(var.grid[var.y - 1], var.x + 1, 1)
+  c3 = substr(var.grid[var.y + 1], var.x + 1, 1)
+  c4 = substr(var.grid[var.y + 1], var.x - 1, 1)
+
+  d1 = "${local.c1}${local.c3}"
+  d2 = "${local.c2}${local.c4}"
+
+  found_d1 = contains(["SM", "MS"], local.d1)
+  found_d2 = contains(["SM", "MS"], local.d2)
+}
+
+output "found" {
+  value = local.found_a && local.found_d1 && local.found_d2
+}

2024/bonus/day04/check_point/check_xmas/main.tf

@@ -0,0 +1,27 @@
+variable "grid" {
+  type = list(string)
+}
+
+variable "x" {
+  type = number
+}
+
+variable "y" {
+  type = number
+}
+
+variable "dx" {
+  type = number
+}
+
+variable "dy" {
+  type = number
+}
+
+locals {
+  match = [for i in range(4) : var.x + i * var.dx >= 0 && try(substr(var.grid[var.y + i * var.dy], var.x + i * var.dx, 1), "F") == substr("XMAS", i, 1)]
+}
+
+output "found" {
+  value = alltrue(local.match) ? 1 : 0
+}

2024/bonus/day04/check_point/main.tf

@@ -0,0 +1,64 @@
+variable "grid" {
+  type = list(string)
+}
+
+variable "index" {
+  type = number
+}
+
+variable "width" {
+  type = number
+}
+
+variable "height" {
+  type = number
+}
+
+locals {
+  x = var.index % var.width
+  y = floor(var.index / var.width)
+
+  directions = {
+    "UL" = [-1, -1]
+    "U"  = [0, -1]
+    "UR" = [1, -1]
+    "L"  = [-1, 0]
+    "R"  = [1, 0]
+    "DL" = [-1, 1]
+    "D"  = [0, 1]
+    "DR" = [1, 1]
+  }
+
+  should_check_x_mas = local.x >= 1 && local.y >= 1 && local.x < var.width - 1 && local.y < var.height - 1
+}
+
+module "check_xmas" {
+  source   = "./check_xmas"
+  for_each = local.directions
+
+  grid = var.grid
+
+  x = local.x
+  y = local.y
+
+  dx = each.value[0]
+  dy = each.value[1]
+}
+
+module "check_x_mas" {
+  source = "./check_x_mas"
+  count  = local.should_check_x_mas ? 1 : 0
+
+  grid = var.grid
+
+  y = local.y
+  x = local.x
+}
+
+output "xmas" {
+  value = sum([for _, v in module.check_xmas : v.found])
+}
+
+output "x_mas" {
+  value = try(module.check_x_mas[0].found, false) ? 1 : 0
+}

2024/bonus/day04/main.tf

@@ -0,0 +1,28 @@
+variable "input" {
+  type = string
+}
+
+locals {
+  grid   = split("\n", chomp(var.input))
+  height = length(local.grid)
+  width  = length(local.grid[0])
+}
+
+module "check_point" {
+  source = "./check_point"
+
+  count = local.width * local.height
+
+  width  = local.width
+  height = local.height
+  grid   = local.grid
+  index  = count.index
+}
+
+output "part1" {
+  value = sum(module.check_point[*].xmas)
+}
+
+output "part2" {
+  value = sum(module.check_point[*].x_mas)
+}

2024/bonus/main.tf

@@ -40,3 +40,9 @@ output "day03_1" {
 output "day03_2" {
   value = module.day03.part2
 }
+
+# Don't run this, it runs out of memory
+# module "day04" {
+#   source = "./day04"
+#   input  = file("../inputs/04.txt")
+# }

2024/bonus/tests.tftest.hcl

@@ -74,3 +74,42 @@ run "day3_2" {
     error_message = "Part2 output is wrong"
   }
 }
+
+run "day4_small" {
+  command = plan
+
+  module {
+    source = "./day04"
+  }
+
+  variables {
+    input = file("../tests/samples/04.1.txt")
+  }
+
+  assert {
+    condition     = output.part1 == 4
+    error_message = "Part1 output is wrong"
+  }
+}
+
+run "day4" {
+  command = plan
+
+  module {
+    source = "./day04"
+  }
+
+  variables {
+    input = file("../tests/samples/04.2.txt")
+  }
+
+  assert {
+    condition     = output.part1 == 18
+    error_message = "Part1 output is wrong"
+  }
+
+  assert {
+    condition     = output.part2 == 9
+    error_message = "Part2 output is wrong"
+  }
+}