y2024d9

y2024/src/bin/d9.rs

@@ -0,0 +1,20 @@
+use std::fs;
+
+use y2024::days::d9;
+
+fn main() {
+    part1();
+    part2();
+}
+
+fn part1() {
+    let root = env!("CARGO_MANIFEST_DIR");
+    let content = fs::read_to_string(format!("{root}/resources/9_input.txt")).unwrap();
+    println!("{}", d9::process_part1(&content));
+}
+
+fn part2() {
+    let root = env!("CARGO_MANIFEST_DIR");
+    let content = fs::read_to_string(format!("{root}/resources/9_input.txt")).unwrap();
+    println!("{}", d9::process_part2(&content));
+}

y2024/src/days/d9.rs

@@ -0,0 +1,129 @@
+pub fn process_part1(input: &str) -> u64 {
+    let mut ids = Vec::new();
+    for (file_id, chunk) in input.trim_end().as_bytes().chunks(2).enumerate() {
+        let byte = chunk[0];
+        for _ in 0..(byte - 48) {
+            ids.push(file_id.to_string());
+        }
+        if let Some(&byte) = chunk.get(1) {
+            for _ in 0..(byte - 48) {
+                ids.push(".".into());
+            }
+        }
+    }
+    let mut ordered = Vec::new();
+    while !ids.is_empty() {
+        let id = ids.remove(0);
+        if id == "." {
+            while let Some(id) = ids.pop() {
+                if id != "." {
+                    ordered.push(id);
+                    break;
+                }
+            }
+        } else {
+            ordered.push(id);
+        }
+    }
+    let mut res = 0;
+    for (multiplier, id) in ordered.iter().enumerate() {
+        res += multiplier * id.parse::<usize>().unwrap();
+    }
+    res as u64
+}
+
+pub fn process_part2(input: &str) -> u64 {
+    let mut ids = Vec::new();
+    for (file_id, chunk) in input.trim_end().as_bytes().chunks(2).enumerate() {
+        let byte = chunk[0];
+        ids.push((file_id.to_string(), byte - 48));
+        if let Some(&byte) = chunk.get(1) {
+            ids.push((".".into(), byte - 48));
+        }
+    }
+    let mut from_idx = ids.len() - 1;
+    loop {
+        if from_idx == 0 {
+            break;
+        }
+        let (id, size) = ids[from_idx].clone();
+        if id == *"." {
+            from_idx -= 1;
+            continue;
+        }
+        let to_idx = if let Some(idx) = ids.iter().position(|id| id.1 >= size && id.0 == ".") {
+            idx
+        } else {
+            from_idx -= 1;
+            continue;
+        };
+        if from_idx < to_idx {
+            from_idx -= 1;
+            continue;
+        }
+        let free_space = ids[to_idx].1;
+        match size.cmp(&free_space) {
+            std::cmp::Ordering::Less => {
+                let remaining_free_space = free_space - size;
+                ids[to_idx].1 = remaining_free_space;
+                ids[from_idx] = (".".to_string(), size);
+                ids.insert(to_idx, (id.clone(), size));
+                from_idx -= 1;
+            }
+            std::cmp::Ordering::Equal => {
+                ids[to_idx] = (id.clone(), size);
+                ids[from_idx] = (".".to_string(), size);
+                from_idx -= 1;
+            }
+            std::cmp::Ordering::Greater => {
+                from_idx -= 1;
+            }
+        }
+    }
+    let mut res = 0;
+    let mut multiplier = 0;
+    for (id, size) in ids.into_iter() {
+        if id == *"." {
+            multiplier += size as usize;
+            continue;
+        }
+        for _idx in 0..size as usize {
+            res += multiplier * id.parse::<usize>().unwrap();
+            multiplier += 1;
+        }
+    }
+    res as u64
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const INPUT_1: &str = "12345";
+    const INPUT_2: &str = "2333133121414131402";
+    const INPUT_3: &str = "23331331214141314020202";
+
+    #[test]
+    fn part1_simple() {
+        let result = process_part1(INPUT_1);
+        assert_eq!(result, 60);
+    }
+
+    #[test]
+    fn part1_complex_1() {
+        let result = process_part1(INPUT_2);
+        assert_eq!(result, 1928);
+    }
+
+    #[test]
+    fn part1_complex_2() {
+        let result = process_part1(INPUT_3);
+        assert_eq!(result, 2842);
+    }
+
+    #[test]
+    fn part2() {
+        let result = process_part2(INPUT_2);
+        assert_eq!(result, 2858)
+    }
+}

y2024/src/days/mod.rs

@@ -1,15 +1,9 @@
 pub mod d1;
-
 pub mod d2;
-
 pub mod d3;
-
 pub mod d4;
-
 pub mod d5;
-
 pub mod d6;
-
 pub mod d7;
-
 pub mod d8;
+pub mod d9;