gleam 2017 up to day 7 part 1

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diff --git a/aoc2017-gleam/src/aoc_2017/day_7.gleam b/aoc2017-gleam/src/aoc_2017/day_7.gleam
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+import gleam/int
+import gleam/io
+import gleam/list
+import gleam/option.{None, Some}
+import gleam/regex.{type Match, Match}
+import gleam/set
+import gleam/string
+
+pub type Program {
+  Program(name: String, weight: Int, supporting: List(String))
+}
+
+pub fn parse(input: String) {
+  let assert Ok(re) = regex.from_string("([a-z]+) \\(([0-9]+)\\)(?> -> (.*))?")
+
+  use match <- list.map(string.split(input, "\n"))
+  case regex.scan(re, match) {
+    [Match(submatches: [Some(name), Some(weight)], ..)] ->
+      Program(name, to_int(weight), [])
+    [Match(submatches: [Some(name), Some(weight), Some(supporting)], ..)] ->
+      Program(name, to_int(weight), string.split(supporting, ", "))
+    _ -> panic as { "couldn't parse" <> match }
+  }
+}
+
+fn to_int(str: String) -> Int {
+  let assert Ok(n) = int.parse(str)
+  n
+}
+
+pub fn pt_1(input: List(Program)) {
+  let supporters = input |> list.map(fn(p) { p.name }) |> set.from_list()
+  let supporting =
+    input |> list.flat_map(fn(p) { p.supporting }) |> set.from_list()
+
+  let assert [base] = set.difference(supporters, supporting) |> set.to_list
+  base
+}
+
+pub fn pt_2(input: List(Program)) {
+  todo as "part 2 not implemented"
+}