Implementation day 8

2020/src/day08.rs

@@ -0,0 +1,123 @@
+use std::convert::Infallible;
+use std::io::Read;
+use std::str::FromStr;
+
+use crate::common::from_lines;
+use crate::Solution;
+
+#[derive(Debug, Copy, Clone)]
+enum Instruction {
+    Acc(i32),
+    Jmp(i32),
+    Nop(i32),
+}
+
+impl FromStr for Instruction {
+    type Err = Infallible;
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        let mut split = s.split(' ');
+
+        let command = split.next().unwrap();
+        let argument: i32 = split.next().unwrap().parse().unwrap();
+
+        let instruction = match command {
+            "nop" => Instruction::Nop(argument),
+            "acc" => Instruction::Acc(argument),
+            "jmp" => Instruction::Jmp(argument),
+            _ => panic!("Unknown command '{}'", command),
+        };
+
+        Ok(instruction)
+    }
+}
+
+fn run_program(program: &[Instruction]) -> (i32, usize) {
+    let mut accumulator = 0;
+    let mut pc = 0;
+    let mut visited = vec![false; program.len()];
+
+    while pc < program.len() {
+        if visited[pc] {
+            return (accumulator, pc);
+        }
+
+        visited[pc] = true;
+
+        match program[pc] {
+            Instruction::Acc(n) => accumulator += n,
+            Instruction::Jmp(n) => {
+                if n > 0 {
+                    pc += n as usize;
+                } else {
+                    pc -= (-n) as usize;
+                }
+                continue;
+            }
+            Instruction::Nop(_) => {}
+        }
+
+        pc += 1;
+    }
+
+    (accumulator, pc)
+}
+
+#[derive(Default)]
+pub struct Day08;
+
+impl Solution for Day08 {
+    fn part1(&mut self, input: &mut dyn Read) -> String {
+        let program: Vec<Instruction> = from_lines(input);
+        run_program(&program).0.to_string()
+    }
+
+    fn part2(&mut self, input: &mut dyn Read) -> String {
+        let mut program: Vec<Instruction> = from_lines(input);
+
+        for i in 0..program.len() {
+            if let Instruction::Nop(n) = program[i] {
+                program[i] = Instruction::Jmp(n);
+
+                let (acc, pc) = run_program(&program);
+
+                if pc == program.len() {
+                    return acc.to_string();
+                }
+
+                program[i] = Instruction::Nop(n);
+            } else if let Instruction::Jmp(n) = program[i] {
+                program[i] = Instruction::Nop(n);
+
+                let (acc, pc) = run_program(&program);
+
+                if pc == program.len() {
+                    return acc.to_string();
+                }
+
+                program[i] = Instruction::Jmp(n);
+            }
+        }
+
+        panic!("No solution found")
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::test_implementation;
+
+    use super::*;
+
+    const SAMPLE: &[u8] = include_bytes!("../samples/08.txt");
+
+    #[test]
+    fn sample_part1() {
+        test_implementation!(Day08, 1, SAMPLE, 5);
+    }
+
+    #[test]
+    fn sample_part2() {
+        test_implementation!(Day08, 2, SAMPLE, 8);
+    }
+}

2020/src/lib.rs

@@ -8,6 +8,7 @@ mod day04;
 mod day05;
 mod day06;
 mod day07;
+mod day08;
 
 pub trait Solution {
     fn part1(&mut self, input: &mut dyn Read) -> String;
@@ -26,6 +27,7 @@ pub fn get_implementation(day: usize) -> Box<dyn Solution> {
         5 => Box::new(day05::Day05::default()),
         6 => Box::new(day06::Day06::default()),
         7 => Box::new(day07::Day07::default()),
+        8 => Box::new(day08::Day08::default()),
         _ => panic!("Unsupported day {}", day),
     }
 }