submit day 15 part 2

src/bin/15.rs

@@ -1,21 +1,62 @@
+use std::collections::HashMap;
+
 advent_of_code::solution!(15);
 
 pub fn part_one(input: &str) -> Option<u32> {
-    let sum = input
-        .split(',')
-        .map(|string| {
-            string
-                .trim()
-                .bytes()
-                .fold(0, |hash, character| ((hash + character as u32) * 17) % 256)
-        })
-        .sum();
-
-    Some(sum)
+    Some(input.trim().split(',').map(hash_string).sum())
 }
 
 pub fn part_two(input: &str) -> Option<u32> {
-    None
+    let mut boxes: HashMap<u32, Vec<(&str, u32)>> = HashMap::new();
+
+    for string in input.trim().split(',') {
+        if *string.as_bytes().last().unwrap() == b'-' {
+            let lens = &string[..string.len() - 1];
+            let box_number = hash_string(lens);
+
+            if let Some(values) = boxes.get_mut(&box_number) {
+                if let Some(index) = values
+                    .iter()
+                    .position(|(current_lens, ..)| *current_lens == lens)
+                {
+                    values.remove(index);
+                }
+            }
+        } else {
+            let lens = &string[..string.len() - 2];
+            let value = string.chars().last().unwrap().to_digit(10).unwrap();
+            let box_number = hash_string(lens);
+
+            let values = boxes.entry(box_number).or_default();
+
+            if let Some((_, value_in_map)) = values
+                .iter_mut()
+                .find(|(current_lens, ..)| *current_lens == lens)
+            {
+                *value_in_map = value;
+            } else {
+                values.push((lens, value));
+            }
+        }
+    }
+
+    Some(
+        boxes
+            .into_iter()
+            .flat_map(|(box_number, values)| {
+                values
+                    .into_iter()
+                    .enumerate()
+                    .map(move |(index, (_, value))| (box_number + 1) * (index as u32 + 1) * value)
+            })
+            .sum(),
+    )
+}
+
+fn hash_string(string: &str) -> u32 {
+    string
+        .bytes()
+        .fold(0, |hash, character| ((hash + character as u32) * 17) % 256)
 }
 
 #[cfg(test)]
@@ -31,6 +72,6 @@ mod tests {
     #[test]
     fn test_part_two() {
         let result = part_two(&advent_of_code::template::read_file("examples", DAY));
-        assert_eq!(result, None);
+        assert_eq!(result, Some(145));
     }
 }