day1: both solutions

src/day1.rs

@@ -0,0 +1,100 @@
+use aoc_runner_derive::aoc;
+use std::io::{BufRead, BufReader, Lines};
+use std::time::{Duration, Instant};
+
+// PROBLEM 1 solution
+#[aoc(day1, part1)]
+pub fn part1(input: &str) -> u64 {
+    let mut val = 50u64;
+    let mut pass = 0u64;
+    let mod_val = 100;
+    for line in input.lines() {
+        let line = line.trim();
+        let (sign, num) = line.split_at(1);
+        let num_val = num.parse::<u64>().unwrap();
+
+        let add_val = match sign.as_bytes()[0] {
+            b'R' => num_val,
+            b'L' => mod_val - (num_val % mod_val),
+            c => panic!("Invalid direction {}", c),
+        };
+        val = (val + add_val) % mod_val;
+        if val == 0 {
+            pass += 1
+        }
+    }
+    pass
+}
+
+// PROBLEM 2 solution
+
+fn advance<const N: i64>(mut start: i64, mut n: i64) -> (i64, i64) {
+    let mut zero_crossings = 0;
+    while n != 0 {
+        if n > 0 {
+            start += 1;
+            if start == 100 {
+                start = 0;
+                zero_crossings += 1;
+            }
+            n -= 1
+        } else {
+            start -= 1;
+            if start == 0 {
+                zero_crossings += 1;
+            }
+            if start == -1 {
+                start = 99;
+            }
+            n += 1
+        }
+    }
+    (start, zero_crossings)
+}
+
+#[aoc(day1, part2)]
+pub fn part2(input: &str) -> i64 {
+    let mut val = 50;
+    let mut pass = 0i64;
+
+    for line in input.lines() {
+        let line = line.trim();
+        let (sign, num) = line.split_at(1);
+        let num_val = num.parse::<i64>().unwrap();
+
+        let (new_val, add_pass) = match sign.as_bytes()[0] {
+            b'R' => advance::<100>(val, num_val),
+            b'L' => advance::<100>(val, -num_val),
+            c => panic!("Invalid direction {}", c),
+        };
+        val = new_val;
+        pass += add_pass;
+    }
+    pass
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::day1::*;
+
+    const EXAMPLE: &str = &"L68
+    L30
+    R48
+    L5
+    R60
+    L55
+    L1
+    L99
+    R14
+    L82";
+
+    #[test]
+    fn problem1_example() {
+        assert_eq!(part1(EXAMPLE), 3);
+    }
+
+    #[test]
+    fn problem2_example() {
+        assert_eq!(part2(EXAMPLE), 6);
+    }
+}