rust(day25): woo day 25

rust/src/day25.rs

@@ -0,0 +1,35 @@
+use std::{time::Duration, time::Instant};
+
+const CONSTANT: usize = 20201227;
+
+pub fn brute_force(card_pubkey: usize) -> usize {
+    let mut card_loop_size = 0;
+    let mut value = 1;
+    while value != card_pubkey {
+        value = value * 7 % CONSTANT;
+        card_loop_size += 1;
+    }
+    card_loop_size
+}
+
+pub fn run(print: bool) -> Duration {
+    let file_string = std::fs::read_to_string("../inputs/25").unwrap();
+    let instant = Instant::now();
+
+    let mut lines = file_string.lines();
+    let card_pubkey: usize = lines.next().unwrap().trim().parse().unwrap();
+    let door_pubkey: usize = lines.next().unwrap().trim().parse().unwrap();
+
+    let card_loop_size = brute_force(card_pubkey);
+
+    let mut part1 = 1;
+    for _ in 0..card_loop_size {
+        part1 = part1 * door_pubkey % CONSTANT;
+    }
+
+    if print {
+        dbg!(part1);
+    }
+
+    instant.elapsed()
+}

rust/src/main.rs

@@ -26,7 +26,7 @@ use nop as day21;
 use nop as day22;
 mod day23;
 use nop as day24;
-use nop as day25;
+mod day25;
 
 fn main() {
     let days = [