day15

src/day15.rs

@@ -0,0 +1,95 @@
+use aoc_runner_derive::{aoc, aoc_generator};
+
+#[aoc_generator(day15)]
+fn parse(input: &str) -> Vec<String> {
+    input.split(',').map(|x| x.into()).collect::<Vec<String>>()
+}
+
+#[aoc(day15, part1)]
+fn part1(input: &Vec<String>) -> u32 {
+    let mut total = 0;
+    for step in input {
+        total += hash(step);
+    }
+
+    total
+}
+
+fn hash(string: &str) -> u32 {
+    let mut cur_val = 0;
+    for char in string.chars() {
+        cur_val += char as u32;
+        cur_val *= 17;
+        cur_val = cur_val % 256;
+    }
+    cur_val
+}
+
+#[aoc(day15, part2)]
+fn part2(input: &Vec<String>) -> usize {
+    let mut boxes: [Vec<(String, usize)>; 256] =
+        std::iter::repeat_with(|| Vec::with_capacity(input.len()))
+            .take(256)
+            .collect::<Vec<_>>()
+            .try_into()
+            .unwrap();
+    for step in input {
+        
+        
+        if let Some(dash) = step.find('-') {
+            let label = &step[0..dash];
+            let box_number = hash(label) as usize;
+            if let Some(position) = boxes[box_number].iter().position(|(l, _)| *l == *label) {
+                boxes[box_number].remove(position);
+            }
+        } else if let Some(equal) = step.find('=') {
+            let label = &step[0..equal];
+            let box_number = hash(label) as usize;
+            let focal_length = &step[equal + 1..].parse::<u32>().unwrap();
+            if let Some(position) = boxes[box_number].iter().position(|(l, _)| *l == *label) {
+                let _ = std::mem::replace(
+                    &mut boxes[box_number][position],
+                    (label.clone().to_string(), *focal_length as usize),
+                );
+            } else {
+                boxes[box_number].push((label.clone().to_string(), *focal_length as usize));
+            }
+        } else {
+            panic!("invalid step AHHH {}", step)
+        }
+    }
+
+    let mut total = 0;
+
+    for (index, lens_box) in boxes.iter().enumerate() {
+        for (slot, (_, focal_len)) in lens_box.iter().enumerate() {
+            total += (index + 1) * (slot + 1) * focal_len;
+        }
+    }
+
+    total
+}
+
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const EX: &str = r"HASH";
+    const EX_2: &str = r"rn=1,cm-,qp=3,cm=2,qp-,pc=4,ot=9,ab=5,pc-,pc=6,ot=7";
+
+    #[test]
+    fn part1_example() {
+        assert_eq!(part1(&parse(EX)), 52);
+    }
+
+    #[test]
+    fn part1_example2() {
+        assert_eq!(part1(&parse(EX_2)), 1320);
+    }
+
+    #[test]
+    fn part2_example2() {
+        assert_eq!(part2(&parse(EX_2)), 145);
+    }
+}

src/lib.rs

@@ -1,3 +1,4 @@
+mod day15;
 mod day14;
 mod day13;
 mod day12;