More 2020 days

Author: Lexicality

Cargo.lock

@@ -14,6 +14,7 @@ default-run = "advent-of-code"
 [dependencies]
 ansi_term = "0.12.1"
 aoc_macros = { path = "./aoc_macros" }
+cached = "0.56.0"
 clap = { version = "4.0.29", features = ["cargo", "derive", "env"] }
 env_logger = "0.11.8"
 hex = "0.4.3"

Cargo.toml

@@ -0,0 +1,127 @@
+// Copyright (c) 2025 Lexi Robinson
+//
+// Licensed under the EUPL, Version 1.2
+//
+// You may not use this work except in compliance with the Licence.
+// You should have received a copy of the Licence along with this work. If not, see:
+// <https://joinup.ec.europa.eu/collection/eupl/eupl-text-eupl-12>.
+// See the Licence for the specific language governing permissions and limitations under the Licence.
+
+use std::{collections::HashSet, str::FromStr};
+
+use itertools::Itertools;
+
+use crate::AoCError;
+
+#[derive(Debug, Clone, Copy)]
+enum Opcode {
+    Acc(i32),
+    Jmp(i32),
+    Nop(i32),
+}
+
+impl FromStr for Opcode {
+    type Err = AoCError;
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        let (opcode, arg) = s
+            .split_once(' ')
+            .ok_or_else(|| AoCError::new(format!("Expected {s} to have a space in it!")))?;
+        let arg = arg.parse()?;
+        Ok(match opcode {
+            "acc" => Self::Acc(arg),
+            "jmp" => Self::Jmp(arg),
+            "nop" => Self::Nop(arg),
+            _ => return Err(AoCError::new(format!("Unexpected opcode {opcode}"))),
+        })
+    }
+}
+
+impl Opcode {
+    fn swapulate(self) -> Self {
+        match self {
+            Self::Acc(_) => self,
+            Self::Jmp(i) => Self::Nop(i),
+            Self::Nop(i) => Self::Jmp(i),
+        }
+    }
+}
+
+#[derive(Debug, Clone, Copy)]
+enum Outcome {
+    InfiniteLoop,
+    Error,
+    Terminated,
+}
+
+fn computate(opcodes: &[Opcode]) -> (Outcome, i32) {
+    let mut pc = 0;
+    let mut acc = 0;
+    let max = opcodes.len();
+    let mut visited_instructions = HashSet::with_capacity(max);
+    log::debug!("Got {max} opcodes!");
+    while pc < max {
+        if !visited_instructions.insert(pc) {
+            log::debug!("Got an infinite loop at {pc}!");
+            return (Outcome::InfiniteLoop, acc);
+        }
+        let opcode = opcodes[pc];
+        log::debug!("pc is at {pc}, acc is {acc}, opcode is {opcode:?}");
+        match opcode {
+            Opcode::Acc(amt) => acc += amt,
+            Opcode::Jmp(offset) => {
+                if let Some(new_pc) = pc.checked_add_signed(offset as isize) {
+                    log::debug!("Jumping to {new_pc}!");
+                    pc = new_pc;
+                    continue;
+                } else {
+                    log::error!("Opcode {opcode:?} set pc below zero!");
+                    return (Outcome::Error, acc);
+                }
+            }
+            Opcode::Nop(_) => (),
+        }
+        pc += 1;
+    }
+    log::debug!("Program terminated with pc at {pc} and acc at {acc}!");
+    (Outcome::Terminated, acc)
+}
+
+pub fn part_1(data: crate::DataIn) -> crate::AoCResult<String> {
+    let opcodes: Vec<Opcode> = data.map(|line| line.parse()).try_collect()?;
+    let (outcome, acc) = computate(&opcodes);
+    assert!(matches!(outcome, Outcome::InfiniteLoop));
+    let ret = acc;
+    Ok(ret.to_string())
+}
+
+pub fn part_2(data: crate::DataIn) -> crate::AoCResult<String> {
+    let opcodes: Vec<Opcode> = data.map(|line| line.parse()).try_collect()?;
+
+    let ret = (0..opcodes.len())
+        .map(|i| {
+            let mut modified = opcodes.clone();
+            modified[i] = modified[i].swapulate();
+            computate(&modified)
+        })
+        .find_map(|(outcome, acc)| match outcome {
+            Outcome::InfiniteLoop => None,
+            _ => Some(acc),
+        })
+        .ok_or(AoCError::new("no modifications worked!"))?;
+
+    Ok(ret.to_string())
+}
+
+inventory::submit!(crate::AoCDay {
+    year: "2020",
+    day: "8",
+    part_1: crate::AoCPart {
+        main: part_1,
+        example: part_1
+    },
+    part_2: Some(crate::AoCPart {
+        main: part_2,
+        example: part_2
+    })
+});