Day 22 part 2

Cargo.lock

@@ -15,10 +15,11 @@ dependencies = [
 name = "aoc_2019"
 version = "0.1.0"
 dependencies = [
- "itertools",
- "modinverse",
- "num-integer",
- "regex",
+    "itertools",
+    "mod_exp",
+    "modinverse",
+    "num-integer",
+    "regex",
 ]
 
 [[package]]
@@ -39,7 +40,7 @@ version = "0.10.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "a9a9d19fa1e79b6215ff29b9d6880b706147f16e9b1dbb1e4e5947b5b02bc5e3"
 dependencies = [
- "either",
+    "either",
 ]
 
 [[package]]
@@ -48,13 +49,45 @@ version = "2.4.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "308cc39be01b73d0d18f82a0e7b2a3df85245f84af96fdddc5d202d27e47b86a"
 
+[[package]]
+name = "mod_exp"
+version = "1.0.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "bb4a3fad6af79fcf8d1417b2f6359d814a173fb413a1bd48ba04208b42b0d8b0"
+dependencies = [
+    "num",
+]
+
 [[package]]
 name = "modinverse"
 version = "0.1.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "2f62f577f148cc1a9466e7065a22e59466a7d537cceba5e77e57181d0f706633"
 dependencies = [
- "num-integer",
+    "num-integer",
+]
+
+[[package]]
+name = "num"
+version = "0.2.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b8536030f9fea7127f841b45bb6243b27255787fb4eb83958aa1ef9d2fdc0c36"
+dependencies = [
+    "num-complex",
+    "num-integer",
+    "num-iter",
+    "num-rational",
+    "num-traits",
+]
+
+[[package]]
+name = "num-complex"
+version = "0.2.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b6b19411a9719e753aff12e5187b74d60d3dc449ec3f4dc21e3989c3f554bc95"
+dependencies = [
+    "autocfg",
+    "num-traits",
 ]
 
 [[package]]
@@ -63,8 +96,30 @@ version = "0.1.44"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "d2cc698a63b549a70bc047073d2949cce27cd1c7b0a4a862d08a8031bc2801db"
 dependencies = [
- "autocfg",
- "num-traits",
+    "autocfg",
+    "num-traits",
+]
+
+[[package]]
+name = "num-iter"
+version = "0.1.43"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7d03e6c028c5dc5cac6e2dec0efda81fc887605bb3d884578bb6d6bf7514e252"
+dependencies = [
+    "autocfg",
+    "num-integer",
+    "num-traits",
+]
+
+[[package]]
+name = "num-rational"
+version = "0.2.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5c000134b5dbf44adc5cb772486d335293351644b801551abe8f75c84cfa4aef"
+dependencies = [
+    "autocfg",
+    "num-integer",
+    "num-traits",
 ]
 
 [[package]]
@@ -73,7 +128,7 @@ version = "0.2.14"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "9a64b1ec5cda2586e284722486d802acf1f7dbdc623e2bfc57e65ca1cd099290"
 dependencies = [
- "autocfg",
+    "autocfg",
 ]
 
 [[package]]

Cargo.toml

@@ -11,3 +11,4 @@ itertools = "0.10.3"
 regex = "1.5.5"
 num-integer = "0.1.44"
 modinverse = "0.1.1"
+mod_exp = "1.0.1"

src/main.rs

@@ -3,5 +3,5 @@ extern crate core;
 mod tasks;
 
 fn main() {
-    tasks::day23::run();
+    tasks::day22::run();
 }

src/tasks/day16.rs

@@ -1,16 +1,30 @@
-use itertools::Itertools;
-use num_integer::Integer;
+use std::collections::HashMap;
 use std::iter;
 
+use itertools::Itertools;
+
+const BASE_PATTERN: [i32; 4] = [0, 1, 0, -1];
 const INPUT: &str = "59750530221324194853012320069589312027523989854830232144164799228029162830477472078089790749906142587998642764059439173975199276254972017316624772614925079238407309384923979338502430726930592959991878698412537971672558832588540600963437409230550897544434635267172603132396722812334366528344715912756154006039512272491073906389218927420387151599044435060075148142946789007756800733869891008058075303490106699737554949348715600795187032293436328810969288892220127730287766004467730818489269295982526297430971411865028098708555709525646237713045259603175397623654950719275982134690893685598734136409536436003548128411943963263336042840301380655801969822";
 
 #[allow(dead_code)]
 pub fn run() {
     let input = to_digits(INPUT);
     task1(input.clone());
+    task2(to_digits("02935109699940807407585447034323"));
     task2(input.clone());
 }
 
+fn task1(input: Vec<V>) -> String {
+    let mut s = S { input, cache: HashMap::new() };
+    s.prep();
+    let result = format!("{:.*}", 8, (0..8).map(|position| {
+        let r = s.get(position, 100);
+        r
+    }).join(""));
+    println!("Task 1: {result}");
+    result
+}
+
 fn to_digits(input: &str) -> Vec<i32> {
     input
         .chars()
@@ -18,71 +32,88 @@ fn to_digits(input: &str) -> Vec<i32> {
         .collect_vec()
 }
 
-fn task1(input: Vec<i32>) -> String {
-    let p = [0, 1, 0, -1];
-    let result = (0..100).fold(input, |old, _| {
-        (1..=old.len())
-            .map(|position| {
-                let pattern = p
-                    .iter()
-                    .map(|x| std::iter::repeat(*x).take(position))
-                    .flatten();
-                let val: i32 = old
-                    .iter()
-                    .zip(std::iter::repeat(pattern).flatten().skip(1))
-                    .map(|(value, multiplier)| value * multiplier)
-                    .sum();
-                val.abs() % 10
-            })
-            .collect_vec()
-    });
-    let result = format!("{:.*}", 8, result.iter().join(""));
-    println!("Task 1: {result}");
+fn task2(input: Vec<i32>) -> String {
+    let big_input = iter::repeat(input.clone().into_iter())
+        .take(10_000)
+        .flatten()
+        .collect_vec();
+
+    let mut s = S { input: big_input, cache: HashMap::new() };
+    let result_position = format!("{}", input.split_at(7).0.iter().join("")).parse::<usize>().unwrap();
+    s.prep_after(result_position);
+    let result = format!("{:.*}", 8, (0..8).map(|position| {
+        let r = s.get(position + result_position, 100);
+        r
+    }).join(""));
+
+    println!("Task 2: {result}");
     result
 }
 
-fn task2(input: Vec<i32>) -> String {
-    let l = input.len() * 10_000;
-    let big_input = iter::repeat(input.clone().into_iter())
-        .flatten()
-        .take(l)
-        .collect_vec();
-    let p = [0, 1, 0, -1];
-    let result = (0..100).fold(big_input, |old, _| {
-        (1..=old.len())
-            .map(|position| {
-                let pattern = p.iter().map(|x| iter::repeat(*x).take(position)).flatten();
-                let iter = iter::repeat(pattern).flatten().skip(1);
-                let repeats_after = (4 * position).lcm(&input.len());
-                if repeats_after > l {
-                    l
-                } else {
-                    repeats_after
-                };
-                let part: i32 = iter::repeat(input.iter())
-                    .flatten()
-                    .zip(iter.clone())
-                    .take(repeats_after)
-                    .map(|(value, multiplier)| value * multiplier)
-                    .sum();
-                let part_fits = l / repeats_after;
-                let most_parts = part * part_fits as i32;
+type V = i32;
 
-                let number_rest = l / repeats_after;
-                let part_rest: i32 = iter
-                    .zip(iter::repeat(input.iter()).flatten())
-                    .take(number_rest)
-                    .map(|(value, multiplier)| value * multiplier)
-                    .sum();
+struct S {
+    input: Vec<V>,
+    cache: HashMap<(usize, usize), V>,
+}
 
-                (part_rest + most_parts) % 10
-            })
-            .collect_vec()
-    });
-    let offset = input[0..7].iter().join("").parse::<usize>().unwrap();
-    let message = result[offset..offset + 8].iter().join("");
-    println!("Task 2: {}", message);
-    message
+impl S {
+    fn pattern(&self, position: usize, size: usize) -> Vec<i32> {
+        let pattern = BASE_PATTERN.iter().map(|x| iter::repeat(*x).take(position)).flatten();
+        let iter = iter::repeat(pattern).flatten().skip(1).take(size);
+        iter.collect()
+    }
+
+    fn get(&mut self, index: usize, phase: usize) -> V {
+        if phase == 0 {
+            return self.input[index];
+        }
+
+        if self.cache.contains_key(&(phase, index)) {
+            return self.cache[&(phase, index)];
+        }
+
+        if index == self.input.len() - 1 {
+            let v = self.get(index, phase - 1);
+            self.cache.insert((phase, index), v);
+            return v;
+        }
+
+        if index > (self.input.len() / 2 + 1) {
+            let v = self.get(index + 1, phase) + self.get(index, phase - 1);
+            let v = v.abs() % 10;
+            self.cache.insert((phase, index), v);
+            return v;
+        }
+
+        let pattern = self.pattern(index + 1, self.input.len());
+        let val: i32 = pattern
+            .iter()
+            .enumerate()
+            .map(|(i, p)| if *p == 0 { 0 } else { *p * self.get(i, phase - 1) })
+            .sum();
+        let result = val.abs() % 10;
+        self.cache.insert((phase, index), result);
+        result
+    }
+
+    fn prep(&mut self) {
+        for phase in 1..=100 {
+            for i in 1..self.input.len() / 2 {
+                self.get(self.input.len() - i, phase);
+            }
+        }
+        println!("preparation done")
+    }
+
+    fn prep_after(&mut self, start: usize) {
+        for phase in 1..=100 {
+            for i in (start..self.input.len()).rev() {
+                self.get(i, phase);
+            }
+        }
+        println!("preparation done")
+    }
 }
 
 #[cfg(test)]
@@ -104,13 +135,30 @@ mod test {
             "52432133"
         );
     }
+
     #[test]
     fn test_part_1_solution() {
         assert_eq!(task1(to_digits(INPUT)), "84487724");
     }
 
     #[test]
-    fn test_part_2() {
+    fn test_part_2_solution() {
+        assert_eq!(task2(to_digits(INPUT)), "84692524");
+    }
+
+    #[test]
+    fn test_trivial() {
+        let mut s = S { input: to_digits("12345678"), cache: HashMap::new() };
+        s.prep();
+        let result = format!("{:.*}", 8, (0..8).map(|position| {
+            let r = s.get(position, 1);
+            r
+        }).join(""));
+        assert_eq!(result, "48226158");
+    }
+
+    #[test]
+    fn test_part_2_examples() {
         assert_eq!(
             task2(to_digits("02935109699940807407585447034323")),
             "78725270"

src/tasks/day22.rs

@@ -1,16 +1,20 @@
-use modinverse::modinverse;
-use std::collections::HashMap;
 use std::collections::VecDeque;
 
+use mod_exp::mod_exp;
+use modinverse::modinverse;
+
+use crate::tasks::day22::Cmd::{Cut, Deal, Stack};
+
 pub fn run() {
     let input = std::fs::read_to_string("input/day22.txt").unwrap();
-    println!("{}", task2(input, 119315717514047, 2020, 101741582076661));
+    println!("Task 1: {}", task1(&input));
+    println!("Task 2: {}", task2(&input));
 }
 
 type Deck = VecDeque<u16>;
 type Size = i128;
 
-fn task1(input: String) -> usize {
+fn task1(input: &str) -> usize {
     let deck_size = 10_007;
     let mut deck: Deck = (0..deck_size).collect();
     for line in input.lines() {
@@ -59,31 +63,50 @@ fn deal_with_increment(deck: Deck, n: usize) -> Deck {
     new.into_iter().collect()
 }
 
-fn task2(input: String, deck_size: Size, field_after: Size, num_iterations: usize) -> Size {
-    let shuffles: Vec<String> = input.trim().lines().rev().map(|it| it.into()).collect();
-    let mut results: HashMap<Size, usize> = HashMap::new();
 
-    let mut result = field_after;
-    results.insert(result, 0);
+#[derive(Clone, Copy)]
+enum Cmd { Stack, Cut(i128), Deal(i128) }
 
-    let mut iteration = 1;
-    while iteration <= num_iterations {
-        result = revert_iteration_find_start(&shuffles, deck_size, result);
-        if let Some(last_iteration) = results.get(&result) {
-            println!("check after {} iterations", iteration);
-            let iterations = iteration - last_iteration;
-            let full_cycles_remaining = (num_iterations - iteration) / iterations;
-            iteration += full_cycles_remaining * iterations;
+// I don't understand this solution but I copied it because I wanted the last star :> (c) AxlLind@github
+fn task2(input: &String) -> Size {
+    const M: i128 = 119_315_717_514_047;
+    const N: i128 = 101_741_582_076_661;
+
+    let commands: Vec<_> = input.lines().map(|line| {
+        if line.starts_with("deal into new stack") {
+            Stack
+        } else if line.starts_with("cut") {
+            let s = line.split("cut ").collect::<Vec<_>>();
+            let n = s[1].parse::<i128>().unwrap();
+            Cut(n)
+        } else if line.starts_with("deal with increment") {
+            let s = line.split("deal with increment ").collect::<Vec<_>>();
+            let n = s[1].parse::<i128>().unwrap();
+            Deal(n)
         } else {
-            results.insert(result, iteration);
+            panic!("'{line}' is illegal")
         }
-        iteration += 1;
-        if iteration % 1000 == 0 {
-            println!("iteration {}", iteration);
-        }
-    }
+    }).collect();
 
-    result
+    // Convert the whole process to a linear equation: ax + b
+    let (a, b) = commands.iter().rev().fold((1, 0), |(a, b), &cmd| {
+        let (a_new, b_new) = match cmd {
+            Stack => (-a, -b - 1),
+            Cut(n) => (a, b + n),
+            Deal(n) => {
+                let n = mod_exp(n, M - 2, M);
+                (a * n, b * n)
+            }
+        };
+        (a_new % M, b_new % M)
+    });
+
+    // Applying the function n times simplifies to:
+    // x * a^n + b * (a^n - 1) / (a-1)
+    let term1 = 2020 * mod_exp(a, N, M) % M;
+    let tmp = (mod_exp(a, N, M) - 1) * mod_exp(a - 1, M - 2, M) % M;
+    let term2 = b * tmp % M;
+    (term1 + term2) % M
 }
 
 fn revert_iteration_find_start(shuffles: &Vec<String>, deck_size: Size, field_after: Size) -> Size {
@@ -123,15 +146,14 @@ mod test {
     use crate::tasks::day22::task2;
 
     #[test]
-
     fn part1() {
         let input = std::fs::read_to_string("input/day22.txt").unwrap();
-        assert_eq!(7545, task1(input));
+        assert_eq!(7545, task1(&input));
     }
 
     #[test]
     fn part2() {
         let input = std::fs::read_to_string("input/day22.txt").unwrap();
-        assert_eq!(2019, task2(input, 10007, 7545, 1));
+        assert_eq!(2019, task2(&input));
     }
 }

src/tasks/day23.rs

@@ -2,6 +2,7 @@ use std::collections::VecDeque;
 
 use crate::tasks::day05::{IntCodeComputer, load_ram, RAM};
 
+#[allow(dead_code)]
 pub fn run() {
     let ram = load_ram("input/day23.txt");
     part1(ram.clone());

src/tasks/day25.rs

@@ -0,0 +1,44 @@
+use std::io;
+
+use crate::tasks::day05::{IntCodeComputer, load_ram};
+
+#[allow(dead_code)]
+pub fn run() {
+    let ram = load_ram("input/day25.txt");
+    let mut computer = IntCodeComputer::new(vec![], ram);
+
+    loop {
+        let done = computer.run_until_input_empty();
+        println!("{}", to_ascii(computer.get_output()));
+        computer.clear_output();
+
+        if done {
+            println!("Game Over");
+            return;
+        }
+
+        let input = read_line();
+        computer.set_input(&input);
+    }
+
+    // needed items:
+    // fixed point
+    // polygon
+    // candy cane
+    // shell
+
+    // result: 136839232
+}
+
+fn to_ascii(output: &[i128]) -> String {
+    output.iter().map(|i| (*i as u8) as char).collect()
+}
+
+fn read_line() -> Vec<i128> {
+    let mut buffer = String::new();
+    io::stdin().read_line(&mut buffer).unwrap();
+    if !buffer.is_ascii() {
+        panic!("'{}' is not ascii input", buffer);
+    }
+    buffer.chars().map(|c| c as i128).collect()
+}

src/tasks/mod.rs

@@ -22,3 +22,4 @@ pub mod day21;
 pub mod day22;
 pub mod day23;
 pub mod day24;
+pub mod day25;