From 52a6d3a28a9f71714bf64b7675e57eaea48a999e Mon Sep 17 00:00:00 2001
From: timeshifter <timeshifter@sumatrae>
Date: Sun, 5 Jul 2026 16:55:34 +0200
Subject: [PATCH] add day 23

---
 day23/Cargo.lock  |   7 +++
 day23/Cargo.toml  |   6 +++
 day23/input.txt   |  47 +++++++++++++++++
 day23/src/main.rs | 127 ++++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 187 insertions(+)
 create mode 100644 day23/Cargo.lock
 create mode 100644 day23/Cargo.toml
 create mode 100644 day23/input.txt
 create mode 100644 day23/src/main.rs

diff --git a/day23/Cargo.lock b/day23/Cargo.lock
new file mode 100644
index 0000000..8dd0414
--- /dev/null
+++ b/day23/Cargo.lock
@@ -0,0 +1,7 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 4
+
+[[package]]
+name = "day23"
+version = "0.1.0"
diff --git a/day23/Cargo.toml b/day23/Cargo.toml
new file mode 100644
index 0000000..4f0aacb
--- /dev/null
+++ b/day23/Cargo.toml
@@ -0,0 +1,6 @@
+[package]
+name = "day23"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
diff --git a/day23/input.txt b/day23/input.txt
new file mode 100644
index 0000000..a2b735a
--- /dev/null
+++ b/day23/input.txt
@@ -0,0 +1,47 @@
+jio a, +18
+inc a
+tpl a
+inc a
+tpl a
+tpl a
+tpl a
+inc a
+tpl a
+inc a
+tpl a
+inc a
+inc a
+tpl a
+tpl a
+tpl a
+inc a
+jmp +22
+tpl a
+inc a
+tpl a
+inc a
+inc a
+tpl a
+inc a
+tpl a
+inc a
+inc a
+tpl a
+tpl a
+inc a
+inc a
+tpl a
+inc a
+inc a
+tpl a
+inc a
+inc a
+tpl a
+jio a, +8
+inc b
+jie a, +4
+tpl a
+inc a
+jmp +2
+hlf a
+jmp -7
diff --git a/day23/src/main.rs b/day23/src/main.rs
new file mode 100644
index 0000000..69b88ed
--- /dev/null
+++ b/day23/src/main.rs
@@ -0,0 +1,127 @@
+fn main() {
+    let instructions: Vec<_> = std::fs::read_to_string("input.txt")
+        .unwrap()
+        .lines()
+        .map(Instruction::parse)
+        .collect();
+
+    // part 1: 307
+    let mut registers = Register::new();
+
+    let result = run_program(&instructions, &mut registers);
+    println!("{result}");
+
+    // part 2
+    let mut registers = Register::new();
+    registers.a = 1;
+
+    let result = run_program(&instructions, &mut registers);
+    println!("{result}");
+}
+
+fn run_program(instructions: &[Instruction], registers: &mut Register) -> u32 {
+    let mut pointer = 0;
+
+    while let Some(instruction) = instructions.get(pointer) {
+        match instruction {
+            Instruction::Hlf(c) => {
+                *registers.get_mut(*c) /= 2;
+                pointer += 1;
+            }
+            Instruction::Tpl(c) => {
+                *registers.get_mut(*c) *= 3;
+                pointer += 1;
+            }
+            Instruction::Inc(c) => {
+                *registers.get_mut(*c) += 1;
+                pointer += 1;
+            }
+            Instruction::Jmp(offset) => {
+                pointer = ((pointer as isize) + *offset) as usize;
+            }
+            Instruction::Jie(c, offset) => {
+                if registers.get(*c).is_multiple_of(2) {
+                    pointer = ((pointer as isize) + *offset) as usize;
+                } else {
+                    pointer += 1;
+                }
+            }
+            Instruction::Jio(c, offset) => {
+                if registers.get(*c) == 1 {
+                    pointer = ((pointer as isize) + *offset) as usize;
+                } else {
+                    pointer += 1;
+                }
+            }
+        }
+    }
+
+    registers.b
+}
+
+#[derive(Debug)]
+struct Register {
+    a: u32,
+    b: u32,
+}
+
+impl Register {
+    fn new() -> Self {
+        Self { a: 0, b: 0 }
+    }
+
+    fn get(&self, c: char) -> u32 {
+        match c {
+            'a' => self.a,
+            'b' => self.b,
+            _ => panic!("unknown register: {c}"),
+        }
+    }
+
+    fn get_mut(&mut self, c: char) -> &mut u32 {
+        match c {
+            'a' => &mut self.a,
+            'b' => &mut self.b,
+            _ => panic!("unknown register: {c}"),
+        }
+    }
+}
+
+#[derive(Debug)]
+enum Instruction {
+    Hlf(char),
+    Tpl(char),
+    Inc(char),
+    Jmp(isize),
+    Jie(char, isize),
+    Jio(char, isize),
+}
+
+impl Instruction {
+    fn parse(s: &str) -> Self {
+        let words: Vec<_> = s.split_whitespace().collect();
+        match words[0] {
+            "hlf" => Self::Hlf(words[1].parse().unwrap()),
+            "tpl" => Self::Tpl(words[1].parse().unwrap()),
+            "inc" => Self::Inc(words[1].parse().unwrap()),
+            "jmp" => Self::Jmp(words[1].parse().unwrap()),
+            "jie" => Self::Jie(
+                words[1]
+                    .chars()
+                    .take_while(|c| c.is_alphabetic())
+                    .next()
+                    .unwrap(),
+                words[2].parse().unwrap(),
+            ),
+            "jio" => Self::Jio(
+                words[1]
+                    .chars()
+                    .take_while(|c| c.is_alphabetic())
+                    .next()
+                    .unwrap(),
+                words[2].parse().unwrap(),
+            ),
+            _ => panic!(),
+        }
+    }
+}