day 4

.tool-versions

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+erlang 27.1.2

sample/day4-sample.txt

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+MMMSXXMASM
+MSAMXMSMSA
+AMXSXMAAMM
+MSAMASMSMX
+XMASAMXAMM
+XXAMMXXAMA
+SMSMSASXSS
+SAXAMASAAA
+MAMMMXMMMM
+MXMXAXMASX

src/day4_p1.gleam

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+import gleam/dict.{type Dict}
+import gleam/int
+import gleam/io
+import gleam/iterator
+import gleam/list.{filter, fold, index_map, map}
+import gleam/string
+import stdin.{stdin}
+
+const word_size = 4
+
+const directions = [#(1, 0), #(1, -1), #(1, 1), #(0, 1)]
+
+pub fn main() {
+  stdin() |> read_input |> find_xmas |> io.debug
+}
+
+fn find_xmas(xmas_map: Dict(#(Int, Int), String)) -> Int {
+  xmas_map
+  |> dict.filter(fn(_, char) { char == "X" || char == "S" })
+  |> dict.keys
+  |> map(fn(coord) {
+    directions
+    |> list.count(fn(dir) {
+      case
+        xmas_map
+        |> dict.take(traverse(coord, dir))
+        |> dict.values
+      {
+        ["X", "M", "A", "S"] -> True
+        ["S", "A", "M", "X"] -> True
+        _ -> False
+      }
+    })
+  })
+  |> fold(0, int.add)
+}
+
+fn traverse(start: #(Int, Int), direction: #(Int, Int)) {
+  let #(s_x, s_y) = start
+
+  direction
+  |> list.repeat(word_size)
+  |> list.index_map(fn(dir, idx) {
+    let #(x, y) = dir
+    #(s_x + x * idx, s_y + y * idx)
+  })
+}
+
+fn read_input(it: iterator.Iterator(String)) -> Dict(#(Int, Int), String) {
+  it
+  |> iterator.to_list
+  |> map(string.trim)
+  |> filter(not(string.is_empty))
+  |> index_map(fn(str, col) {
+    str
+    |> string.to_graphemes
+    |> index_map(fn(char, row) { #(#(row, col), char) })
+  })
+  |> list.flatten
+  |> dict.from_list
+}
+
+fn not(a: fn(a) -> Bool) {
+  fn(param: a) -> Bool { !a(param) }
+}

src/day4_p2.gleam

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+import gleam/dict.{type Dict}
+import gleam/io
+import gleam/iterator
+import gleam/list.{count, filter, index_map, map}
+import gleam/string
+import stdin.{stdin}
+
+pub fn main() {
+  stdin() |> read_input |> find_xmas |> io.debug
+}
+
+fn find_xmas(xmas_map: Dict(#(Int, Int), String)) -> Int {
+  xmas_map
+  |> dict.filter(fn(_, char) { char == "A" })
+  |> dict.keys
+  |> count(fn(coord) {
+    coord
+    |> traverse
+    |> list.all(fn(keys) {
+      case
+        xmas_map
+        |> dict.take(keys)
+        |> dict.values
+      {
+        ["M", "S"] -> True
+        ["S", "M"] -> True
+        _ -> False
+      }
+    })
+  })
+}
+
+fn traverse(start: #(Int, Int)) {
+  let #(x, y) = start
+  [[#(x - 1, y - 1), #(x + 1, y + 1)], [#(x - 1, y + 1), #(x + 1, y - 1)]]
+}
+
+fn read_input(it: iterator.Iterator(String)) -> Dict(#(Int, Int), String) {
+  it
+  |> iterator.to_list
+  |> map(string.trim)
+  |> filter(not(string.is_empty))
+  |> index_map(fn(str, col) {
+    str
+    |> string.to_graphemes
+    |> index_map(fn(char, row) { #(#(row, col), char) })
+  })
+  |> list.flatten
+  |> dict.from_list
+}
+
+fn not(a: fn(a) -> Bool) {
+  fn(param: a) -> Bool { !a(param) }
+}