From b9a480c97aa597dbd345eef96de4097f4742ca0f Mon Sep 17 00:00:00 2001
From: Louis Vallat <contact@louis-vallat.dev>
Date: Tue, 10 Dec 2024 00:21:01 +0100
Subject: [PATCH] feat: added day 9 part 1 and 2

Signed-off-by: Louis Vallat <contact@louis-vallat.dev>
---
 .gitea/workflows/build_and_run.yml |   2 +-
 day9/Cargo.toml                    |   6 ++
 day9/src/main.rs                   | 118 +++++++++++++++++++++++++++++
 3 files changed, 125 insertions(+), 1 deletion(-)
 create mode 100644 day9/Cargo.toml
 create mode 100644 day9/src/main.rs

diff --git a/.gitea/workflows/build_and_run.yml b/.gitea/workflows/build_and_run.yml
index a70ba0c..97ca62c 100644
--- a/.gitea/workflows/build_and_run.yml
+++ b/.gitea/workflows/build_and_run.yml
@@ -11,7 +11,7 @@ jobs:
     name: Challenge for day
     strategy:
       matrix:
-        day_number: [1, 2, 3, 4, 5, 6, 7, 8]
+        day_number: [1, 2, 3, 4, 5, 6, 7, 8, 9]
     runs-on: rust-bookworm
     steps:
       - name: Check out repository code
diff --git a/day9/Cargo.toml b/day9/Cargo.toml
new file mode 100644
index 0000000..48c42be
--- /dev/null
+++ b/day9/Cargo.toml
@@ -0,0 +1,6 @@
+[package]
+name = "day9"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
diff --git a/day9/src/main.rs b/day9/src/main.rs
new file mode 100644
index 0000000..4d070e6
--- /dev/null
+++ b/day9/src/main.rs
@@ -0,0 +1,118 @@
+use std::collections::{HashSet, LinkedList};
+use std::{env, fs};
+
+fn read_input(path: &str) -> String {
+    fs::read_to_string(path).expect("Cannot read file.")
+}
+
+fn parse_input(input: &str) -> LinkedList<(Option<usize>, usize)> {
+    let mut nodes = LinkedList::new();
+    let mut is_file = true;
+    let mut id = 0;
+
+    for x in input.chars().filter_map(|c| c.to_digit(10)) {
+        if x != 0 {
+            if is_file {
+                nodes.push_back((Some(id), x as usize));
+                id += 1;
+            } else {
+                nodes.push_back((None, x as usize));
+            }
+        }
+        is_file = !is_file;
+    }
+
+    nodes
+}
+
+fn checksum<'a, I>(nodes: I) -> usize
+where
+    I: IntoIterator<Item = &'a (Option<usize>, usize)>,
+{
+    let mut index = 0;
+    let mut sum = 0;
+    for node in nodes {
+        if let Some(id) = node.0 {
+            sum += (node.1 * ((id * index) + (id * (index + node.1 - 1)))) / 2;
+        }
+        index += node.1;
+    }
+    sum
+}
+
+fn part_1(disk_map: &LinkedList<(Option<usize>, usize)>) -> usize {
+    let mut disk_map = disk_map.clone();
+    let mut defragmented = LinkedList::new();
+    let mut free_len = 0;
+    while let Some(node) = disk_map.pop_front() {
+        if node.0.is_some() {
+            defragmented.push_back(node);
+        } else {
+            let to_place = node.1;
+            free_len += to_place;
+            while let Some(node) = disk_map.pop_back() {
+                if let Some(id) = node.0 {
+                    if node.1 > to_place {
+                        defragmented.push_back((Some(id), to_place));
+                        disk_map.push_back((Some(id), node.1 - to_place));
+                    } else {
+                        if node.1 < to_place {
+                            disk_map.push_front((None, to_place - node.1));
+                            free_len -= to_place - node.1;
+                        }
+                        defragmented.push_back(node);
+                    }
+                    break;
+                } else {
+                    free_len += node.1;
+                }
+            }
+        }
+    }
+
+    defragmented.push_back((None, free_len));
+    checksum(&defragmented)
+}
+
+fn part_2(disk_map: &LinkedList<(Option<usize>, usize)>) -> usize {
+    let mut disk_map = Vec::from_iter(disk_map.clone());
+    let mut defragmented_ids = HashSet::new();
+    let mut i = disk_map.len() - 1;
+
+    while i > 0 {
+        let id = disk_map[i].0.unwrap_or_default();
+        if disk_map[i].0.is_some() && !defragmented_ids.contains(&id) {
+            defragmented_ids.insert(id);
+            let needed_space = disk_map[i].1;
+            for j in 0..i {
+                if disk_map[j].0.is_none() {
+                    let available_space = disk_map[j].1;
+                    if available_space >= needed_space {
+                        disk_map.swap(i, j);
+                        if available_space > needed_space {
+                            disk_map.insert(j + 1, (None, available_space - needed_space));
+                            disk_map[j].1 = needed_space;
+                            disk_map[i + 1].1 = needed_space;
+                            i += 1;
+                        }
+                        break;
+                    }
+                }
+            }
+        }
+        i -= 1;
+    }
+
+    checksum(&disk_map)
+}
+
+fn main() {
+    let args: Vec<String> = env::args().collect();
+    for arg in args.iter().skip(1) {
+        let input = read_input(&arg);
+        let disk_map = parse_input(&input);
+        println!("[{}]", &arg);
+        println!("\t[Part 1] => Answer is '{}'.", part_1(&disk_map));
+        println!("\t[Part 2] => Answer is '{}'.", part_2(&disk_map));
+    }
+}