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authorHJ <thechairman@thechairman.info>2023-12-09 01:25:44 -0500
committerHJ <thechairman@thechairman.info>2023-12-09 01:25:44 -0500
commit2f570466b75ca76636a692006bec59cbb3a038cf (patch)
tree880c0facb899178e25ea070e42d10d666d4e6ad1 /aoc2023/src
parentb51dd4b3768bce0209733ef2562cb96e5330d3c6 (diff)
downloadgleam_aoc-2f570466b75ca76636a692006bec59cbb3a038cf.tar.gz
gleam_aoc-2f570466b75ca76636a692006bec59cbb3a038cf.zip
day 9 complete
Diffstat (limited to 'aoc2023/src')
-rw-r--r--aoc2023/src/day9/.gitignore1
-rw-r--r--aoc2023/src/day9/solve.gleam69
2 files changed, 70 insertions, 0 deletions
diff --git a/aoc2023/src/day9/.gitignore b/aoc2023/src/day9/.gitignore
new file mode 100644
index 0000000..ae40cea
--- /dev/null
+++ b/aoc2023/src/day9/.gitignore
@@ -0,0 +1 @@
+input.txt \ No newline at end of file
diff --git a/aoc2023/src/day9/solve.gleam b/aoc2023/src/day9/solve.gleam
new file mode 100644
index 0000000..ce061ae
--- /dev/null
+++ b/aoc2023/src/day9/solve.gleam
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+import adglent.{First, Second}
+import gleam/io
+import gleam/list
+import gleam/string
+import gleam/int
+
+fn parse(input: String, backwards backwards: Bool) -> List(List(Int)) {
+ use line <- list.map(string.split(input, "\n"))
+ use n_str <- list.map(maybe_backwards(string.split(line, " "), backwards))
+ let assert Ok(n) = int.parse(n_str)
+ n
+}
+
+fn maybe_backwards(xs: List(a), backwards: Bool) -> List(a) {
+ case backwards {
+ False -> list.reverse(xs)
+ True -> xs
+ }
+}
+
+fn is_constant(ns: List(Int)) -> Bool {
+ case list.unique(ns) {
+ [_] -> True
+ _ -> False
+ }
+}
+
+fn take_derivative(ns: List(Int)) -> List(Int) {
+ ns
+ |> list.window_by_2
+ |> list.map(fn(tup) { tup.0 - tup.1 })
+}
+
+fn extrapolate(ns: List(Int)) {
+ case is_constant(ns), ns {
+ True, [n, ..] -> n
+ False, [n, ..] -> n + extrapolate(take_derivative(ns))
+ }
+}
+
+fn part(input: String, backwards backwards: Bool) {
+ input
+ |> parse(backwards: backwards)
+ |> list.fold(0, fn(acc, ns) { extrapolate(ns) + acc })
+ |> string.inspect
+}
+
+pub fn part1(input: String) {
+ part(input, backwards: False)
+}
+
+pub fn part2(input: String) {
+ part(input, backwards: True)
+}
+
+pub fn main() {
+ let assert Ok(part) = adglent.get_part()
+ let assert Ok(input) = adglent.get_input("9")
+ case part {
+ First ->
+ part1(input)
+ |> adglent.inspect
+ |> io.println
+ Second ->
+ part2(input)
+ |> adglent.inspect
+ |> io.println
+ }
+}