day 15 in the books

data/examples/15.txt

@@ -0,0 +1 @@
+rn=1,cm-,qp=3,cm=2,qp-,pc=4,ot=9,ab=5,pc-,pc=6,ot=7

src/bin/15.rs

@@ -0,0 +1,93 @@
+advent_of_code::solution!(15);
+
+fn hash_it(s: &str) -> usize {
+    s.as_bytes()
+        .iter()
+        .map(|x| *x as usize)
+        .fold(0, |acc, x| (acc + x) * 17 % 256)
+}
+
+pub fn part_one(input: &str) -> Option<u64> {
+    let sum = input
+        .lines()
+        .next()
+        .unwrap()
+        .split(',')
+        .map(hash_it)
+        .sum::<usize>();
+    Some(sum as u64)
+}
+
+enum Op {
+    Rem,
+    Set(usize),
+}
+
+impl Op {
+    fn from(s: &str) -> Self {
+        match s.chars().next().unwrap() {
+            '-' => Self::Rem,
+            '=' => {
+                let num = &s[1..2]
+                    .parse::<usize>()
+                    .expect("= should be followed by number");
+                Self::Set(*num)
+            }
+            _ => panic!("Unexpected op {}", s),
+        }
+    }
+}
+
+pub fn part_two(input: &str) -> Option<u64> {
+    let mut boxes: Vec<Vec<(String, usize)>> = vec![Vec::new(); 256];
+    input.lines().next().unwrap().split(',').for_each(|s| {
+        let len = if s.chars().last().unwrap() == '-' {
+            s.len() - 1
+        } else {
+            s.len() - 2
+        };
+        let label = &s[0..len];
+        let hash_val = hash_it(label);
+        let op = Op::from(&s[len..]);
+        if let Some(index) = boxes[hash_val].iter().position(|item| item.0 == label) {
+            match op {
+                Op::Rem => {
+                    boxes[hash_val].remove(index);
+                }
+                Op::Set(x) => {
+                    boxes[hash_val][index] = (label.to_owned(), x);
+                }
+            }
+        } else if let Op::Set(x) = op {
+            boxes[hash_val].push((label.to_owned(), x));
+        }
+    });
+    let sum = boxes
+        .iter()
+        .enumerate()
+        .map(|(num, v)| {
+            v.iter()
+                .enumerate()
+                .map(|(index, item)| (1 + num) * (1 + index) * item.1)
+                .sum::<usize>()
+        })
+        .sum::<usize>();
+    Some(sum as u64)
+}
+
+#[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(1320));
+    }
+
+    #[test]
+    fn test_part_two() {
+        let result = part_two(&advent_of_code::template::read_file("examples", DAY));
+        assert_eq!(result, Some(145));
+    }
+}