From aa65136b9296a27379ce1edd53daa2a23390f748 Mon Sep 17 00:00:00 2001
From: Louis Vallat <contact@louis-vallat.dev>
Date: Thu, 9 Jan 2025 09:53:14 +0100
Subject: [PATCH] feat: added day 22 part 1 and 2

Signed-off-by: Louis Vallat <contact@louis-vallat.dev>
---
 .gitea/workflows/build_and_run.yml |  2 +-
 day22/Cargo.toml                   |  6 +++
 day22/src/main.rs                  | 66 ++++++++++++++++++++++++++++++
 3 files changed, 73 insertions(+), 1 deletion(-)
 create mode 100644 day22/Cargo.toml
 create mode 100644 day22/src/main.rs

diff --git a/.gitea/workflows/build_and_run.yml b/.gitea/workflows/build_and_run.yml
index 5444adb..6a96701 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, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21]
+        day_number: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22]
     runs-on: rust-bookworm
     steps:
       - name: Check out repository code
diff --git a/day22/Cargo.toml b/day22/Cargo.toml
new file mode 100644
index 0000000..07fb531
--- /dev/null
+++ b/day22/Cargo.toml
@@ -0,0 +1,6 @@
+[package]
+name = "day22"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
diff --git a/day22/src/main.rs b/day22/src/main.rs
new file mode 100644
index 0000000..36d30fe
--- /dev/null
+++ b/day22/src/main.rs
@@ -0,0 +1,66 @@
+use std::{env, fs};
+
+const ITERATIONS: usize = 2000;
+
+fn xor_shift(mut secret: i64) -> i64 {
+    secret ^= secret << 6;
+    secret &= (1 << 24) - 1;
+    secret ^= secret >> 5;
+    secret ^= secret << 11;
+    secret &= (1 << 24) - 1;
+    secret
+}
+
+fn read_input(path: &str) -> String {
+    fs::read_to_string(path).expect("Cannot read file.")
+}
+
+fn parse_input(input: &str) -> Vec<i64> {
+    input
+        .lines()
+        .filter(|line| !line.is_empty())
+        .map(|line| line.parse().unwrap())
+        .collect()
+}
+
+fn compute_market(secrets: &Vec<i64>) -> (i64, i64) {
+    let mut secrets_sum = 0;
+    let (mut last_monkey, mut cache) = (vec![None; 160000], vec![0; 160000]);
+
+    for (monkey, &secret) in secrets.iter().enumerate() {
+        let mut secret = secret;
+        let mut previous_price = 0;
+        let mut a;
+        let (mut b, mut c, mut d) = (0, 0, 0);
+
+        for i in 0..ITERATIONS {
+            secret = xor_shift(secret);
+            let price = secret % 10;
+            (a, b, c, d) = (b, c, d, 9 + price - previous_price);
+
+            if i > 2 {
+                let key = (a * 6859 + b * 361 + c * 19 + d) as usize;
+                if last_monkey[key].is_none() || last_monkey[key].unwrap() != monkey {
+                    last_monkey[key] = Some(monkey);
+                    cache[key] += price;
+                }
+            }
+            previous_price = price;
+        }
+        secrets_sum += secret;
+    }
+
+    (secrets_sum, *cache.iter().max().unwrap())
+}
+
+fn main() {
+    let args: Vec<String> = env::args().collect();
+    for arg in args.iter().skip(1) {
+        let input = read_input(&arg);
+        let secrets = parse_input(&input);
+        let (secrets_sum, best_price) = compute_market(&secrets);
+        println!("[{}]", &arg);
+        println!("\t[Part 1] => Answer is '{}'.", secrets_sum);
+        println!("\t[Part 2] => Answer is '{}'.", best_price);
+    }
+}