Add solution for "Day 1: Secret Entrance", part 2

src/solvers/secret_entrance.rs

@@ -6,9 +6,30 @@ pub struct SecretEntrance {}
 impl SecretEntrance {
     const START_POSITION: i32 = 50;
     const DIAL_SIZE: i32 = 100;
-    const COUNT_POSITION: i32 = 0;
+    const ZERO_POSITION: i32 = 0;
     const POSITIVE_SIGN_CHAR: char = 'R';
     const NEGATIVE_SIGN_CHAR: char = 'L';
+
+    fn update_position(
+        position: i32,
+        distance: i32,
+        mut zero_hits: u64,
+        mut zero_passes: u64,
+    ) -> (i32, u64, u64) {
+        let mut new_position = position + distance;
+        let rounds = new_position.div_euclid(Self::DIAL_SIZE);
+        zero_passes += u64::try_from(rounds.abs()).unwrap();
+        new_position -= Self::DIAL_SIZE * rounds;
+        if new_position == Self::ZERO_POSITION {
+            zero_hits += 1;
+            if position != Self::ZERO_POSITION && distance < 0 {
+                zero_passes += 1;
+            }
+        } else if position == Self::ZERO_POSITION && distance < 0 {
+            zero_passes -= 1;
+        }
+        (new_position, zero_hits, zero_passes)
+    }
 }
 
 impl Solver for SecretEntrance {
@@ -17,26 +38,26 @@ impl Solver for SecretEntrance {
 
     fn process_data<R: BufRead>(&self, reader: R) -> (u64, u64) {
         let mut position = Self::START_POSITION;
-        let mut count = 0;
-        let format = format!(
+        let mut zero_hits = 0;
+        let mut zero_passes = 0;
+        let format: String = format!(
             "{{[{}{}]}}{{d}}",
             Self::POSITIVE_SIGN_CHAR,
             Self::NEGATIVE_SIGN_CHAR
         );
         for line in reader.lines().map_while(Result::ok) {
-            if let Ok((sign, distance)) = scan_fmt!(&line, &format, char, i32) {
-                position = (position
-                    + if sign == Self::POSITIVE_SIGN_CHAR {
-                        distance
-                    } else {
-                        -distance
-                    })
-                .rem_euclid(Self::DIAL_SIZE);
-            }
-            if position == Self::COUNT_POSITION {
-                count = count + 1;
-            }
+            let (sign, distance) = scan_fmt!(&line, &format, char, i32).unwrap();
+            (position, zero_hits, zero_passes) = Self::update_position(
+                position,
+                if sign == Self::POSITIVE_SIGN_CHAR {
+                    distance
+                } else {
+                    -distance
+                },
+                zero_hits,
+                zero_passes,
+            );
         }
-        (count, 0)
+        (zero_hits, zero_passes)
     }
 }