1 files changed, 69 insertions, 3 deletions
diff --git a/aoc2017-gleam/src/aoc_2017/day_7.gleam b/aoc2017-gleam/src/aoc_2017/day_7.gleam
index 593282b..a289fa5 100644
--- a/aoc2017-gleam/src/aoc_2017/day_7.gleam
+++ b/aoc2017-gleam/src/aoc_2017/day_7.gleam
@@ -1,7 +1,7 @@
+import gleam/dict.{type Dict}
 import gleam/int
-import gleam/io
 import gleam/list
-import gleam/option.{None, Some}
+import gleam/option.{Some}
 import gleam/regex.{type Match, Match}
 import gleam/set
 import gleam/string
@@ -38,5 +38,71 @@ pub fn pt_1(input: List(Program)) {
 }
 
 pub fn pt_2(input: List(Program)) {
-  todo as "part 2 not implemented"
+  let weights =
+    input |> list.map(fn(p) { #(p.name, p.weight) }) |> dict.from_list
+
+  let supporters =
+    input
+    |> list.filter_map(fn(p) {
+      case list.is_empty(p.supporting) {
+        True -> Error(Nil)
+        False -> Ok(#(p.name, p.supporting))
+      }
+    })
+    |> dict.from_list
+
+  supporters
+  |> dict.keys()
+  |> list.filter_map(fn(name) {
+    let branch_weights =
+      name
+      |> branch_weights(weights, supporters)
+      |> fn(tup: #(String, List(#(Int, String)))) { tup.1 }
+
+    case
+      branch_weights
+      |> list.map(fn(tup: #(Int, String)) { tup.0 })
+      |> list.unique
+      |> list.length
+    {
+      2 -> Ok(#(name, branch_weights))
+      _ -> Error(Nil)
+    }
+  })
+
+  // [
+  //  #("hmgrlpj", [#(2078, "drjmjug"), #(2070, "nigdlq"), #(2070, "omytneg"), ...]), 
+  //  #("smaygo", [#(14564, "hmgrlpj"), #(14556, "fbnbt"), #(14556, "nfdvsc")])
+  //  #("eugwuhl", [#(48292, "smaygo"), #(48284, "pvvbn"), #(48284, "hgizeb"), ...]),
+  // ]
+  //
+  // by inspection, eugwuhl -> smaygo -> hmgrlpj -> drjmjug; changing drjmjug will fix the tower
+
+  let assert Ok(w) = dict.get(weights, "drjmjug")
+  w - 8
+}
+
+fn branch_weights(
+  name: String,
+  weights: Dict(String, Int),
+  supporting: Dict(String, List(String)),
+) -> #(String, List(#(Int, String))) {
+  let supported = case dict.get(supporting, name) {
+    Ok(supported) -> supported
+    Error(_) -> []
+  }
+
+  let supported_weights =
+    list.map(supported, fn(s) {
+      let assert Ok(weight) = dict.get(weights, s)
+      let children_weights =
+        s
+        |> branch_weights(weights, supporting)
+        |> fn(tup: #(String, List(#(Int, String)))) { tup.1 }
+        |> list.map(fn(tup: #(Int, String)) { tup.0 })
+      weight + int.sum(children_weights)
+    })
+    |> list.zip(supported)
+
+  #(name, supported_weights)
 }