Added AOC 2020 day 21 - 25

www/statics/aoc/2020/25_solution.rs

@@ -0,0 +1,76 @@
+use crate::common::AdventOfCodeDay;
+
+pub struct Day25 {
+    pkey_card: u64,
+    pkey_door: u64,
+}
+
+impl Day25 {
+    pub fn new() -> Self {
+        let input_bytes = include_bytes!("../res/25_input.txt");
+        let input_str = String::from_utf8_lossy(input_bytes);
+        
+        let lines = input_str
+                        .lines()
+                        .map(|p| String::from(p))
+                        .map(|p| p.parse::<u64>().unwrap())
+                        .collect::<Vec<_>>();
+
+        Self {
+            pkey_card: lines[0],
+            pkey_door: lines[1],
+        }
+    }
+}
+
+impl Day25 {
+    fn transform(subjectnumber: u64, loopcount: usize) -> u64 {
+        let mut v = 1;
+        for _ in 0..loopcount {
+            v *= subjectnumber;
+            v %= 20201227;
+        }
+        return v;
+    }
+
+    fn transform_back(subjectnumber: u64, pkey_dest: u64) -> usize {
+        let mut v = 1;
+        for lc in 1.. {
+            v *= subjectnumber;
+            v %= 20201227;
+
+            if v == pkey_dest {
+                return lc;
+            }
+        }
+        panic!();
+    }
+}
+
+impl AdventOfCodeDay for Day25 {
+
+    fn task_1(&self) -> String {
+
+        verboseln!("card public key: {}", self.pkey_card);
+        verboseln!("door public key: {}", self.pkey_door);
+        verboseln!();
+
+        let loopsize_card = Self::transform_back(7, self.pkey_card);
+        verboseln!("card loop size: {}", loopsize_card);
+        let loopsize_door = Self::transform_back(7, self.pkey_door);
+        verboseln!("door loop size: {}", loopsize_door);
+        verboseln!();
+
+        let skey_card = Self::transform(self.pkey_card, loopsize_door);
+        verboseln!("card encryption key: {}", skey_card);
+        let skey_door = Self::transform(self.pkey_door, loopsize_card);
+        verboseln!("door encryption key: {}", skey_door);
+        verboseln!();
+
+        return skey_card.to_string().to_owned();
+    }
+
+    fn task_2(&self) -> String  {
+        return "".to_owned()
+    }
+}