1 files changed, 69 insertions, 0 deletions
diff --git a/25/src/main.rs b/25/src/main.rs
new file mode 100644
index 0000000..1fd0149
--- /dev/null
+++ b/25/src/main.rs
@@ -0,0 +1,69 @@
+use advent_lib::prelude::*;
+
+//use std::collections::BTreeSet;
+//use std::convert::TryFrom;
+
+
+
+fn main() -> Result<()> {
+  let mut args = std::env::args();
+  if args.len() != 2 {
+    eprintln!("Usage: advent input");
+  }
+  let _ = args.next();
+  let filename = args.next().unwrap();
+
+  let input = advent_lib::read_lines_file(&filename)?;
+
+  let card_public = input[0].parse::<i64>().unwrap();
+  let door_public = input[1].parse::<i64>().unwrap();
+  let subject: i64 = 7;
+
+  let mut i = 0;
+  let mut value = 1;
+  let mut card_loop_size = None;
+  let mut door_loop_size = None;
+  loop {
+    value = iterate(value, subject);
+    i += 1;
+
+    if card_loop_size.is_none() {
+      if value == card_public {
+        card_loop_size = Some(i);
+      }
+    }
+
+    if door_loop_size.is_none() {
+      if value == door_public {
+        door_loop_size = Some(i);
+      }
+    }
+
+    if card_loop_size.is_some() && door_loop_size.is_some() {
+      break;
+    }
+  }
+
+  let key = transform(door_public, card_loop_size.unwrap());
+
+  println!("{}", key);
+
+  Ok(())
+}
+
+
+fn iterate(input: i64, subject: i64) -> i64 {
+  let mut output = input * subject;
+  output %= 20201227;
+  output
+}
+
+
+fn transform(subject: i64, loop_count: usize) -> i64 {
+  let mut value = 1;
+  for _ in 0 .. loop_count {
+    value = iterate(value, subject);
+  }
+  value
+}
+