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import gleam/io
import gleam/int
import gleam/list
import gleam/bool
import gleam/result as res
import gleam/set.{Set}
import gleam/iterator.{Iterator} as iter
import gleam/option.{None, Option, Some} as opt
import ext/listx
import ext/resultx as resx
import util/input_util
import util/parser as p
type Instr {
Acc(increment: Int)
Jmp(offset: Int)
Nop(unused: Int)
}
type Program =
List(Instr)
type Cpu {
Cpu(acc: Int, pc: Int)
}
const initial_cpu = Cpu(acc: 0, pc: 0)
type ExecutionResult {
InfiniteLoop(acc_before_second: Int)
Termination(acc_after: Int)
}
fn parse_program(lines: List(String)) -> Program {
let argument_parser =
p.any(of: [
p.replace(p.literal("+"), with: 1),
p.replace(p.literal("-"), with: -1),
])
|> p.then(p.int())
|> p.map2(with: int.multiply)
let instr_parser =
p.any(of: [
p.literal("acc ")
|> p.proceed(with: argument_parser)
|> p.map(with: Acc),
p.literal("jmp ")
|> p.proceed(with: argument_parser)
|> p.map(with: Jmp),
p.literal("nop ")
|> p.proceed(with: argument_parser)
|> p.map(with: Nop),
])
lines
|> list.map(with: fn(line) {
line
|> p.parse_entire(with: instr_parser)
|> resx.assert_unwrap
})
}
fn fetch(from program: Program, with cpu: Cpu) -> Option(Instr) {
program
|> list.at(cpu.pc)
|> opt.from_result
}
fn execute(instr: Instr, on cpu: Cpu) -> Cpu {
case instr {
Acc(increment) -> Cpu(cpu.acc + increment, cpu.pc + 1)
Jmp(offset) -> Cpu(cpu.acc, cpu.pc + offset)
Nop(_) -> Cpu(cpu.acc, cpu.pc + 1)
}
}
fn execution_result_helper(
program: Program,
cpu: Cpu,
visited: Set(Int),
) -> ExecutionResult {
use <- bool.guard(
when: set.contains(visited, cpu.pc),
return: InfiniteLoop(acc_before_second: cpu.acc),
)
case fetch(from: program, with: cpu) {
None -> Termination(acc_after: cpu.acc)
Some(instr) ->
execution_result_helper(
program,
execute(instr, on: cpu),
set.insert(visited, cpu.pc),
)
}
}
fn execution_result(program: Program) -> ExecutionResult {
execution_result_helper(program, initial_cpu, set.new())
}
fn halts(program: Program) -> Bool {
case execution_result(program) {
Termination(_) -> True
_ -> False
}
}
fn all_program_mutations(of program: Program) -> Iterator(Program) {
let undo_corruption = fn(instr) {
case instr {
Nop(offset) -> Jmp(offset)
Jmp(unused) -> Nop(unused)
other -> other
}
}
program
|> iter.from_list
|> iter.index
|> iter.flat_map(fn(elem) {
let #(index, instr) = elem
case instr {
Acc(_) -> iter.empty()
_ ->
program
|> listx.set(undo_corruption(instr), at: index)
|> iter.single
}
})
}
fn part1(lines: List(String)) -> Int {
let assert InfiniteLoop(acc) =
lines
|> parse_program
|> execution_result
acc
}
fn part2(lines: List(String)) -> Int {
let assert Ok(Termination(acc)) =
lines
|> parse_program
|> all_program_mutations
|> iter.find(one_that: halts)
|> res.map(with: execution_result)
acc
}
pub fn main() -> Nil {
let test = input_util.read_lines("test08")
let assert 5 = part1(test)
let assert 8 = part2(test)
let input = input_util.read_lines("day08")
io.debug(part1(input))
io.debug(part2(input))
Nil
}
|
