Add day9

day9/Cargo.lock

@@ -0,0 +1,7 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 4
+
+[[package]]
+name = "day9"
+version = "0.1.0"

day9/Cargo.toml

@@ -0,0 +1,6 @@
+[package]
+name = "day9"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]

day9/src/main.rs

@@ -0,0 +1,119 @@
+use std::{cmp::Ordering, fmt::Display};
+
+#[derive(Debug, Clone, Eq, PartialEq)]
+struct Space {
+    id: Option<usize>,
+}
+
+impl Display for Space {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(
+            f,
+            "{}",
+            if let Some(i) = self.id {
+                i.to_string()
+            } else {
+                ".".to_string()
+            }
+        )
+    }
+}
+
+impl PartialOrd for Space {
+    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
+        Some(self.cmp(other))
+    }
+}
+
+impl Ord for Space {
+    fn cmp(&self, other: &Self) -> std::cmp::Ordering {
+        if self.id.is_none() {
+            return Ordering::Less;
+        }
+        if other.id.is_none() {
+            return Ordering::Greater;
+        }
+        self.id.unwrap().cmp(&other.id.unwrap())
+    }
+}
+
+fn parse(input: &str) -> Vec<Space> {
+    input
+        .chars()
+        .enumerate()
+        .filter(|(_, c)| c.is_ascii_digit())
+        .flat_map(|(c_idx, c)| {
+            (0..c.to_digit(10).unwrap()).map(move |_| Space {
+                id: if c_idx % 2 == 0 {
+                    Some(c_idx / 2)
+                } else {
+                    None
+                },
+            })
+        })
+        .collect()
+}
+
+fn checksum(filesystem: &[Space]) -> usize {
+    filesystem
+        .iter()
+        .enumerate()
+        .map(|(c_idx, c)| if let Some(v) = c.id { c_idx * v } else { 0 })
+        .sum()
+}
+
+fn part1(filesystem: &mut [Space]) -> usize {
+    for space_idx in 0..filesystem.len() {
+        if filesystem[space_idx].id.is_none() {
+            let last = filesystem
+                .iter()
+                .enumerate()
+                .rev()
+                .find(|(_, n)| n.id.is_some())
+                .unwrap();
+            if last.0 < space_idx {
+                break;
+            }
+            filesystem.swap(space_idx, last.0);
+        };
+    }
+    checksum(filesystem)
+}
+
+fn get_chunk_size(filesystem: &[Space], idx: usize) -> usize {
+    let mut chunk_size = 0;
+    while idx + chunk_size < filesystem.len() && filesystem[idx + chunk_size] == filesystem[idx] {
+        chunk_size += 1;
+    }
+    chunk_size
+}
+
+fn part2(filesystem: &mut [Space]) -> usize {
+    for move_id in (0..=filesystem.iter().max().unwrap().id.unwrap()).rev() {
+        let move_idx = filesystem
+            .iter()
+            .enumerate()
+            .find(|(_, c)| c.id.unwrap_or(move_id + 1) == move_id)
+            .unwrap()
+            .0;
+        let move_chunk_size = get_chunk_size(filesystem, move_idx);
+        for free_idx in 0..move_idx {
+            if filesystem[free_idx].id.is_some() {
+                continue;
+            }
+            if get_chunk_size(filesystem, free_idx) >= move_chunk_size {
+                for i in 0..move_chunk_size {
+                    filesystem.swap(move_idx + i, free_idx + i);
+                }
+                break;
+            }
+        }
+    }
+    checksum(filesystem)
+}
+
+fn main() {
+    let mut input = parse(include_str!("../input.txt"));
+    println!("{}", part1(&mut input.clone()));
+    println!("{}", part2(&mut input));
+}