From 33b9bb932d76a2b314dc9db9be4fd76e77c3ed72 Mon Sep 17 00:00:00 2001
From: Himangshu Saikia <himangshu.saikia.iitg@gmail.com>
Date: Sun, 22 Dec 2024 06:56:26 +0100
Subject: [PATCH] 2024_22

---
 src/bin/2024_22/main.rs | 111 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 111 insertions(+)
 create mode 100644 src/bin/2024_22/main.rs

diff --git a/src/bin/2024_22/main.rs b/src/bin/2024_22/main.rs
new file mode 100644
index 0000000..f191aff
--- /dev/null
+++ b/src/bin/2024_22/main.rs
@@ -0,0 +1,111 @@
+use std::{collections::HashMap, ops::BitXor};
+
+use aoc::{common, io};
+
+fn mix(secret: usize, b: usize) -> usize {
+    secret.bitxor(b)
+}
+
+fn prune(secret: usize) -> usize {
+    secret % 16777216
+}
+
+fn generate(n: usize, times: usize) -> usize {
+    if times == 0 {
+        return n;
+    }
+
+    let mut secret = n;
+    let a = secret * 64;
+    secret = mix(secret, a);
+    secret = prune(secret);
+    let b = secret / 32;
+    secret = mix(secret, b);
+    secret = prune(secret);
+    let c = secret * 2048;
+    secret = mix(secret, c);
+    secret = prune(secret);
+    generate(secret, times - 1)
+}
+
+fn generate_lst(lst: &mut Vec<usize>, times: usize) {
+    if times == 0 {
+        return;
+    }
+
+    let mut secret = *lst.last().unwrap();
+    let n2 = secret * 64;
+    secret = mix(secret, n2);
+    secret = prune(secret);
+    let n4 = secret / 32;
+    secret = mix(secret, n4);
+    secret = prune(secret);
+    let n6 = secret * 2048;
+    secret = mix(secret, n6);
+    secret = prune(secret);
+    lst.push(secret);
+    generate_lst(lst, times - 1)
+}
+
+fn solve<const PART: usize>(input: &str) -> usize {
+    let mut ans = 0;
+    let mut map: HashMap<(i64, i64, i64, i64, usize), usize> = HashMap::new();
+    for (i, ns) in input.lines().enumerate() {
+        let number: usize = io::parse_num(ns);
+
+        if PART == 1 {
+            ans += generate(number, 2000);
+        } else {
+            let mut lst = vec![number];
+            generate_lst(&mut lst, 2000);
+            let lst_dig: Vec<usize> = lst
+                .iter()
+                .map(|n| n.to_string().chars().last().unwrap().to_digit(10).unwrap() as usize)
+                .collect();
+            let diff: Vec<(i64, usize)> = lst_dig
+                .iter()
+                .zip(lst_dig.iter().skip(1))
+                .map(|(a, b)| (*b as i64 - *a as i64, *b))
+                .collect();
+
+            for w in diff.windows(4) {
+                let key = (w[0].0, w[1].0, w[2].0, w[3].0, i);
+                map.entry(key).or_insert(w[3].1);
+            }
+        }
+    }
+
+    if PART == 1 {
+        return ans;
+    }
+    let mut total_map: HashMap<(i64, i64, i64, i64), usize> = HashMap::new();
+    for ((k1, k2, k3, k4, _), v) in map.iter() {
+        if let Some(b) = total_map.get_mut(&(*k1, *k2, *k3, *k4)) {
+            *b += *v;
+        } else {
+            total_map.insert((*k1, *k2, *k3, *k4), *v);
+        }
+    }
+
+    *total_map.values().max().unwrap()
+}
+
+fn main() {
+    let input = common::get_input();
+    println!("{input:?}");
+    common::timed(&input, solve::<1>, true);
+    common::timed(&input, solve::<2>, false);
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_samples() {
+        let sample_input1 = "1\n10\n100\n2024";
+        assert_eq!(solve::<1>(sample_input1), 37327623);
+        let sample_input2 = "1\n2\n3\n2024";
+        assert_eq!(solve::<2>(sample_input2), 23);
+    }
+}