From 0042d2fbcd479a8e343b273d7909f88a03f1040e Mon Sep 17 00:00:00 2001
From: Araozu <fernando@araozu.dev>
Date: Thu, 25 Apr 2024 20:04:24 -0500
Subject: [PATCH] Rewrite day 8 in rust for fun & profit

---
 rust/08/computer.rs | 137 ++++++++++++++++++++++++++++++++++++++++++++
 rust/08/main.rs     |  53 +++++++++++++++++
 2 files changed, 190 insertions(+)
 create mode 100644 rust/08/computer.rs
 create mode 100644 rust/08/main.rs

diff --git a/rust/08/computer.rs b/rust/08/computer.rs
new file mode 100644
index 0000000..a8262f3
--- /dev/null
+++ b/rust/08/computer.rs
@@ -0,0 +1,137 @@
+pub struct Computer {
+    instructions: Vec<Instruction>,
+    ip: usize,
+    acc: i32,
+    flipped_idx: Option<usize>,
+}
+
+enum Instruction {
+    Acc(i32),
+    Jmp(i32),
+    Nop(i32),
+}
+
+impl Computer {
+    /// Creates a new computer from a string containing intructions
+    pub fn new(input: String) -> Computer {
+        let instructions: Vec<Instruction> = input
+            .split("\n")
+            .map(|line| {
+                let inst = &line[..3];
+                let sign_value = match &line[4..5] {
+                    "+" => 1,
+                    "-" => -1,
+                    _ => panic!("Expected + or -, got something else"),
+                };
+                let value_str = &line[5..];
+                let value = sign_value
+                    * value_str
+                        .parse::<i32>()
+                        .expect(format!("Found an invalid number: {}", value_str).as_str());
+
+                match inst {
+                    "acc" => Instruction::Acc(value),
+                    "jmp" => Instruction::Jmp(value),
+                    "nop" => Instruction::Nop(value),
+                    _ => panic!("Found an invalid instruction: {}", inst),
+                }
+            })
+            .collect();
+
+        Computer {
+            instructions,
+            ip: 0,
+            acc: 0,
+            flipped_idx: None,
+        }
+    }
+
+    /// Returns the number of instructions of this computer
+    pub fn len(&self) -> usize {
+        self.instructions.len()
+    }
+
+    /// Executes the instruction at the current ip
+    pub fn step(&mut self) {
+        match self.instructions.get(self.ip) {
+            Some(Instruction::Acc(value)) => {
+                self.acc += value;
+                self.ip += 1;
+            }
+            Some(Instruction::Jmp(value)) => {
+                let ip_i32: i32 = self.ip.try_into().expect("Found an invalid ip");
+                let new_value = ip_i32 + value;
+
+                self.ip = new_value.try_into().expect("Tried to assign an invalid ip");
+            }
+            Some(Instruction::Nop(_)) => {
+                self.ip += 1;
+            }
+            None => {
+                panic!("Tried to execute an out of bounds instruction.")
+            }
+        }
+    }
+
+    /// Flips a JMP into NOP, or NOP into JMP instruction at position `idx`.
+    ///
+    /// If this function is called more than once, it panics.
+    pub fn flip(&mut self, idx: usize) {
+        match self.flipped_idx {
+            Some(_) => panic!("An instruction on this computer has already been flipped."),
+            None => {
+                self.flipped_idx = Some(idx);
+                self.flip_instruction(idx);
+            }
+        }
+    }
+
+    /// Internal implementation of flip
+    fn flip_instruction(&mut self, idx: usize) {
+        match self.instructions.get(idx) {
+            Some(Instruction::Jmp(v)) => {
+                self.instructions[idx] = Instruction::Nop(*v);
+            }
+            Some(Instruction::Nop(v)) => {
+                self.instructions[idx] = Instruction::Jmp(*v);
+            }
+            Some(_) => {}
+            None => {
+                panic!(
+                    "Tried to flip an instruction on an out of bounds index. {}",
+                    idx
+                )
+            }
+        }
+    }
+
+    /// Returns whether the instruction at `idx` is JMP or NOP.
+    pub fn jmp_or_nop_at(&mut self, idx: usize) -> bool {
+        match self.instructions.get(idx) {
+            Some(Instruction::Nop(_)) => true,
+            Some(Instruction::Jmp(_)) => true,
+            _ => false,
+        }
+    }
+
+    /// Returns the current ip
+    pub fn get_current_ip(&self) -> usize {
+        self.ip
+    }
+
+    /// Returns the current acc
+    pub fn get_acc(&self) -> i32 {
+        self.acc
+    }
+
+    /// Resets the state of the computer, including any JMP/NOP flip.
+    pub fn reset(&mut self) {
+        self.ip = 0;
+        self.acc = 0;
+
+        if let Some(idx) = self.flipped_idx {
+            self.flipped_idx = None;
+            self.flip_instruction(idx);
+        }
+    }
+}
diff --git a/rust/08/main.rs b/rust/08/main.rs
new file mode 100644
index 0000000..5806661
--- /dev/null
+++ b/rust/08/main.rs
@@ -0,0 +1,53 @@
+use std::{collections::HashMap, fs::read_to_string};
+
+mod computer;
+
+fn main() {
+    // current time
+    let start = std::time::Instant::now();
+
+    let input = read_to_string("input.txt").expect("Input file not found");
+    let mut computer = computer::Computer::new(input);
+
+    let computer_len = computer.len();
+
+    'outer: for i in 0..(computer_len) {
+        // If the instruction at position `i` can't be flipped
+        if !computer.jmp_or_nop_at(i) {
+            continue;
+        }
+
+        // Stores the indexes already executed.
+        let mut map: HashMap<usize, bool> = HashMap::new();
+        computer.flip(i);
+
+        loop {
+            let current_ip = computer.get_current_ip();
+
+            // Success condition
+            if current_ip == computer_len {
+                println!("Result: {}", computer.get_acc());
+                break 'outer;
+            }
+
+            // Loop detected
+            if map.contains_key(&current_ip) {
+                break;
+            }
+
+            // Store current ip to keep track of what instructions have been executed
+            map.insert(current_ip, true);
+
+            // Run the current instruction
+            computer.step();
+        }
+
+        // Reset the computer state
+        computer.reset();
+    }
+
+    // Print the time it took to run the program
+    println!("Time: {} micros", start.elapsed().as_micros());
+
+    println!("No result was found");
+}