Day 2 part 1

Author: timocp

src/adventofcode2024.gleam

@@ -6,6 +6,7 @@ import argv
 import simplifile
 
 import day1
+import day2
 
 pub fn main() {
   case argv.load().arguments {
@@ -14,7 +15,7 @@ pub fn main() {
         Ok(n) -> run(n)
         Error(_) -> io.println("Invalid day: " <> arg)
       }
-    _ -> list.range(1, 1) |> list.each(fn(n) { run(n) })
+    _ -> list.range(1, 2) |> list.each(fn(n) { run(n) })
   }
 }
 
@@ -24,6 +25,7 @@ fn run(n: Int) -> Nil {
   io.print(output("Part 1: "))
   io.println(case n {
     1 -> day1.part1(input) |> int.to_string
+    2 -> day2.part1(input) |> int.to_string
     _ -> "(not implemented)"
   })
   io.print(output("Part 2: "))

src/day2.gleam

@@ -0,0 +1,36 @@
+import gleam/int
+import gleam/list
+import gleam/string
+
+pub fn part1(input: String) -> Int {
+  input |> parse_input |> list.count(safe)
+}
+
+fn safe(report: List(Int)) -> Bool {
+  increasing(report) || decreasing(report)
+}
+
+fn increasing(report: List(Int)) -> Bool {
+  case report {
+    [first, second, ..rest] ->
+      second > first && second - first <= 3 && increasing([second, ..rest])
+    _ -> True
+  }
+}
+
+fn decreasing(report: List(Int)) -> Bool {
+  case report {
+    [first, second, ..rest] ->
+      second < first && first - second <= 3 && decreasing([second, ..rest])
+    _ -> True
+  }
+}
+
+fn parse_input(input: String) -> List(List(Int)) {
+  input
+  |> string.split("\n")
+  |> list.filter(fn(line) { line != "" })
+  |> list.map(fn(line) {
+    line |> string.split(" ") |> list.filter_map(fn(str) { int.parse(str) })
+  })
+}

test/day2_test.gleam

@@ -0,0 +1,20 @@
+import gleeunit
+import gleeunit/should
+
+import day2
+
+pub fn main() {
+  gleeunit.main()
+}
+
+const example1 = "7 6 4 2 1
+1 2 7 8 9
+9 7 6 2 1
+1 3 2 4 5
+8 6 4 4 1
+1 3 6 7 9
+"
+
+pub fn part1_test() {
+  day2.part1(example1) |> should.equal(2)
+}