From d848d977c6b0ca0ea82c8570c48573a5821024e5 Mon Sep 17 00:00:00 2001
From: Lars Martens <lars@martens.red>
Date: Wed, 18 Dec 2024 07:08:15 +0100
Subject: [PATCH] Solve 17.1

---
 src/bin/17.rs | 147 ++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 147 insertions(+)
 create mode 100644 src/bin/17.rs

diff --git a/src/bin/17.rs b/src/bin/17.rs
new file mode 100644
index 0000000..cd7bdde
--- /dev/null
+++ b/src/bin/17.rs
@@ -0,0 +1,147 @@
+use aoc::assert_example;
+use itertools::Itertools;
+
+const INPUT: &str = include_str!("../../input/17");
+
+fn main() {
+    assert_example!(part1, "17-test", "5,7,3,0");
+    println!("Part 1: {}", part1(INPUT));
+    assert_example!(part2, "17-test", 117440);
+    println!("Part 2: {}", part2(INPUT));
+}
+
+fn part1(input: &str) -> String {
+    let mut computer = Computer::parse(input);
+    computer.run();
+    computer.output.iter().map(usize::to_string).join(",")
+}
+
+fn part2(_input: &str) -> usize {
+    0
+}
+
+#[derive(Clone)]
+struct Computer {
+    a: usize,
+    b: usize,
+    c: usize,
+    program: Vec<usize>,
+    ip: usize,
+    output: Vec<usize>,
+}
+
+impl Computer {
+    fn run(&mut self) {
+        while !self.is_halted() {
+            self.step();
+        }
+    }
+
+    fn step(&mut self) {
+        match self.opcode() {
+            0 => {
+                let exp = self.combo_operand().try_into().unwrap();
+                self.a /= 2usize.pow(exp);
+                self.ip += 2;
+            }
+            1 => {
+                self.b ^= self.literal_operand();
+                self.ip += 2;
+            }
+            2 => {
+                self.b = self.combo_operand() % 8;
+                self.ip += 2;
+            }
+            3 => {
+                if self.a == 0 {
+                    self.ip += 2;
+                } else {
+                    self.ip = self.literal_operand();
+                }
+            }
+            4 => {
+                self.b ^= self.c;
+                self.ip += 2;
+            }
+            5 => {
+                self.output.push(self.combo_operand() % 8);
+                self.ip += 2;
+            }
+            6 => {
+                let exp = self.combo_operand().try_into().unwrap();
+                self.b = self.a / 2usize.pow(exp);
+                self.ip += 2;
+            }
+            7 => {
+                let exp = self.combo_operand().try_into().unwrap();
+                self.c = self.a / 2usize.pow(exp);
+                self.ip += 2;
+            }
+            other => panic!("invalid instruction {other}"),
+        }
+    }
+
+    fn is_halted(&self) -> bool {
+        self.ip >= self.program.len()
+    }
+
+    fn opcode(&self) -> usize {
+        self.program[self.ip]
+    }
+
+    fn literal_operand(&self) -> usize {
+        self.program[self.ip + 1]
+    }
+
+    fn combo_operand(&self) -> usize {
+        match self.literal_operand() {
+            n @ 0..=3 => n,
+            4 => self.a,
+            5 => self.b,
+            6 => self.c,
+            other => panic!("invalid combo operand {other}"),
+        }
+    }
+
+    fn parse(input: &str) -> Self {
+        let mut lines = input.lines();
+        let a = lines
+            .next()
+            .unwrap()
+            .strip_prefix("Register A: ")
+            .unwrap()
+            .parse()
+            .unwrap();
+        let b = lines
+            .next()
+            .unwrap()
+            .strip_prefix("Register B: ")
+            .unwrap()
+            .parse()
+            .unwrap();
+        let c = lines
+            .next()
+            .unwrap()
+            .strip_prefix("Register C: ")
+            .unwrap()
+            .parse()
+            .unwrap();
+        lines.next();
+        let program = lines
+            .next()
+            .unwrap()
+            .strip_prefix("Program: ")
+            .unwrap()
+            .split(',')
+            .map(|x| x.parse().unwrap())
+            .collect();
+        Self {
+            a,
+            b,
+            c,
+            program,
+            ip: 0,
+            output: Vec::new(),
+        }
+    }
+}