Solve Day 1: Secret Entrance

README.md

@@ -6,6 +6,14 @@ Solutions for [Advent of Code](https://adventofcode.com/) in [Rust](https://www.
 
 <!--- advent_readme_stars table --->
 
+<!--- benchmarking table --->
+## Benchmarks
+
+| Day | Part 1 | Part 2 |
+| :---: | :---: | :---:  |
+| [Day 1](./src/bin/01.rs) | `113.0µs` | `119.9µs` |
+
+**Total: 0.23ms**
 <!--- benchmarking table --->
 
 ---

data/examples/01.txt

@@ -0,0 +1,11 @@
+L68
+L30
+R48
+L5
+R60
+L55
+L1
+L99
+R14
+L82
+

src/bin/01.rs

@@ -0,0 +1,98 @@
+advent_of_code::solution!(1);
+
+pub fn part_one(input: &str) -> Option<u64> {
+    let mut position: i32 = 50;
+    let mut count = 0u64;
+
+    for line in input.lines() {
+        let line = line.trim();
+        if line.is_empty() {
+            continue;
+        }
+
+        let direction = &line[0..1];
+        let distance: i32 = line[1..].parse().ok()?;
+
+        match direction {
+            "L" => position = (position - distance).rem_euclid(100),
+            "R" => position = (position + distance).rem_euclid(100),
+            _ => return None,
+        }
+
+        if position == 0 {
+            count += 1;
+        }
+    }
+
+    Some(count)
+}
+
+pub fn part_two(input: &str) -> Option<u64> {
+    let mut position: i32 = 50;
+    let mut count = 0u64;
+
+    for line in input.lines() {
+        let line = line.trim();
+        if line.is_empty() {
+            continue;
+        }
+
+        let direction = &line[0..1];
+        let distance: i32 = line[1..].parse().ok()?;
+
+        // Count how many times we pass through 0 during this rotation
+        let zeros = match direction {
+            "L" => {
+                // Moving left: we hit 0 at clicks p, p+100, p+200, ... (if p > 0)
+                // or at clicks 100, 200, 300, ... (if p = 0)
+                if position == 0 {
+                    distance / 100
+                } else if distance >= position {
+                    (distance - position) / 100 + 1
+                } else {
+                    0
+                }
+            }
+            "R" => {
+                // Moving right: we hit 0 at click (100-p), then (100-p)+100, etc.
+                // or at clicks 100, 200, 300, ... (if p = 0)
+                if position == 0 {
+                    distance / 100
+                } else if distance >= 100 - position {
+                    (distance + position - 100) / 100 + 1
+                } else {
+                    0
+                }
+            }
+            _ => return None,
+        };
+
+        count += zeros as u64;
+
+        // Update position
+        match direction {
+            "L" => position = (position - distance).rem_euclid(100),
+            "R" => position = (position + distance).rem_euclid(100),
+            _ => {}
+        }
+    }
+
+    Some(count)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_part_one() {
+        let result = part_one(&advent_of_code::template::read_file("examples", DAY));
+        assert_eq!(result, Some(3));
+    }
+
+    #[test]
+    fn test_part_two() {
+        let result = part_two(&advent_of_code::template::read_file("examples", DAY));
+        assert_eq!(result, Some(6));
+    }
+}