day 02: initial commit

src/advent_of_code.gleam

@@ -2,16 +2,35 @@ import gleam/int
 import gleam/io
 import gleam/result
 import historian_hysteria as day01
+import red_nosed_reports as day02
 import simplifile.{read}
 
 pub fn main() {
   //  Day 01
-  result.map(read("data/day1.txt"), fn(data) {
-    io.println(
-      "[1] Historian Hysteria (Part 1): " <> int.to_string(day01.solve_a(data)),
-    )
-    io.println(
-      "[1] Historian Hysteria (Part 2): " <> int.to_string(day01.solve_b(data)),
-    )
-  })
+  result.unwrap(
+    result.map(read("data/day1.txt"), fn(data) {
+      io.println(
+        "[1] Historian Hysteria (Part 1): "
+        <> int.to_string(day01.solve_a(data)),
+      )
+      io.println(
+        "[1] Historian Hysteria (Part 2): "
+        <> int.to_string(day01.solve_b(data)),
+      )
+    }),
+    Nil,
+  )
+
+  //  Day 02
+  result.unwrap(
+    result.map(read("data/day2.txt"), fn(data) {
+      io.println(
+        "[2] Red Nosed Reports (Part 1): " <> int.to_string(day02.solve_a(data)),
+      )
+      io.println(
+        "[2] Red Nosed Reports (Part 2): " <> int.to_string(day02.solve_b(data)),
+      )
+    }),
+    Nil,
+  )
 }

src/red_nosed_reports.gleam

@@ -0,0 +1,66 @@
+import gleam/int
+import gleam/io
+import gleam/list
+import gleam/pair
+import gleam/result
+import gleam/string
+
+fn parse_line(line: String) -> List(Int) {
+  use a <- list.map(string.split(line, " "))
+  result.unwrap(int.parse(a), 0)
+}
+
+fn all_incr(report: List(Int)) -> Bool {
+  use nums <- list.all(list.window_by_2(report))
+  case pair.second(nums) - pair.first(nums) {
+    x if x > 0 && x < 4 -> True
+    _ -> False
+  }
+}
+
+fn all_decr(report: List(Int)) -> Bool {
+  use nums <- list.all(list.window_by_2(report))
+  case pair.first(nums) - pair.second(nums) {
+    x if x > 0 && x < 4 -> True
+    _ -> False
+  }
+}
+
+fn valid(report: List(Int)) -> Bool {
+  all_incr(report) || all_decr(report)
+}
+
+fn valid_after_dampener(report) -> Bool {
+  case valid(report) {
+    True -> True
+    False -> {
+      let indexed_list = list.index_map(report, fn(x, i) { #(i, x) })
+      let range = list.range(0, list.length(indexed_list) - 1)
+      let final_list =
+        list.map(range, fn(rmi) {
+          use #(_, flist) <- result.map(list.key_pop(indexed_list, rmi))
+          list.map(flist, pair.second)
+        })
+
+      let ys = list.map(final_list, fn(y) { result.unwrap(y, []) })
+      list.any(ys, fn(y) { valid(y) })
+    }
+  }
+}
+
+pub fn solve_a(input: String) -> Int {
+  input
+  |> string.trim()
+  |> string.split("\n")
+  |> list.map(parse_line)
+  |> list.count(valid(_))
+}
+
+pub fn solve_b(input: String) -> Int {
+  input
+  |> string.trim()
+  |> string.split("\n")
+  |> list.map(parse_line)
+  |> list.filter(valid_after_dampener(_))
+  |> list.length()
+}

test/red_nosed_reports_test.gleam

@@ -0,0 +1,21 @@
+import gleam/string
+import gleeunit/should
+import red_nosed_reports as day01
+
+fn test_data() -> String {
+  string.join(
+    [
+      "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",
+    ],
+    "\n",
+  )
+}
+
+pub fn solve_a_test() {
+  should.equal(day01.solve_a(test_data()), 2)
+}
+
+pub fn solve_b_test() {
+  should.equal(day01.solve_b(test_data()), 4)
+}