2020-12-08

# Day 08: Handheld Halting

Description:
--- Day 8: Handheld Halting ---

Your flight to the major airline hub reaches cruising altitude without incident. While you consider checking the in-flight menu for one of those drinks that come with a little umbrella, you are interrupted by the kid sitting next to you.

Their handheld game console won't turn on! They ask if you can take a look.

You narrow the problem down to a strange infinite loop in the boot code (your puzzle input) of the device. You should be able to fix it, but first you need to be able to run the code in isolation.

The boot code is represented as a text file with one instruction per line of text. Each instruction consists of an operation (acc, jmp, or nop) and an argument (a signed number like +4 or -20).

acc increases or decreases a single global value called the accumulator by the value given in the argument. For example, acc +7 would increase the accumulator by 7. The accumulator starts at 0. After an acc instruction, the instruction immediately below it is executed next.
jmp jumps to a new instruction relative to itself. The next instruction to execute is found using the argument as an offset from the jmp instruction; for example, jmp +2 would skip the next instruction, jmp +1 would continue to the instruction immediately below it, and jmp -20 would cause the instruction 20 lines above to be executed next.
nop stands for No OPeration - it does nothing. The instruction immediately below it is executed next.

For example, consider the following program:

nop +0
acc +1
jmp +4
acc +3
jmp -3
acc -99
acc +1
jmp -4
acc +6

These instructions are visited in this order:

nop +0 | 1
acc +1 | 2, 8(!)
jmp +4 | 3
acc +3 | 6
jmp -3 | 7
acc -99 |
acc +1 | 4
jmp -4 | 5
acc +6 |

First, the nop +0 does nothing. Then, the accumulator is increased from 0 to 1 (acc +1) and jmp +4 sets the next instruction to the other acc +1 near the bottom. After it increases the accumulator from 1 to 2, jmp -4 executes, setting the next instruction to the only acc +3. It sets the accumulator to 5, and jmp -3 causes the program to continue back at the first acc +1.

This is an infinite loop: with this sequence of jumps, the program will run forever. The moment the program tries to run any instruction a second time, you know it will never terminate.

Immediately before the program would run an instruction a second time, the value in the accumulator is 5.

Run your copy of the boot code. Immediately before any instruction is executed a second time, what value is in the accumulator?

--- Part Two ---

After some careful analysis, you believe that exactly one instruction is corrupted.

Somewhere in the program, either a jmp is supposed to be a nop, or a nop is supposed to be a jmp. (No acc instructions were harmed in the corruption of this boot code.)

The program is supposed to terminate by attempting to execute an instruction immediately after the last instruction in the file. By changing exactly one jmp or nop, you can repair the boot code and make it terminate correctly.

For example, consider the same program from above:

nop +0
acc +1
jmp +4
acc +3
jmp -3
acc -99
acc +1
jmp -4
acc +6

If you change the first instruction from nop +0 to jmp +0, it would create a single-instruction infinite loop, never leaving that instruction. If you change almost any of the jmp instructions, the program will still eventually find another jmp instruction and loop forever.

However, if you change the second-to-last instruction (from jmp -4 to nop -4), the program terminates! The instructions are visited in this order:

nop +0 | 1
acc +1 | 2
jmp +4 | 3
acc +3 |
jmp -3 |
acc -99 |
acc +1 | 4
nop -4 | 5
acc +6 | 6

After the last instruction (acc +6), the program terminates by attempting to run the instruction below the last instruction in the file. With this change, after the program terminates, the accumulator contains the value 8 (acc +1, acc +1, acc +6).

Fix the program so that it terminates normally by changing exactly one jmp (to nop) or nop (to jmp). What is the value of the accumulator after the program terminates?

Input:
acc +37
acc -1
nop +512
acc +0
jmp +60
acc -3
nop +317
jmp +130
acc +22
acc +34
jmp +486
acc -18
nop +610
acc -14
nop +274
jmp +439
acc -6
acc -1
acc -4
acc +7
jmp +175
nop +179
jmp +197
jmp +76
acc -1
acc +24
jmp +472
acc +8
acc -15
acc +0
jmp +551
acc +46
acc +27
jmp +1
acc +45
jmp +153
acc +14
jmp +207
jmp +1
jmp +557
nop +424
jmp +571
nop -19
nop +9
acc +2
acc +29
jmp +14
acc -10
acc +43
acc +43
jmp +75
jmp +311
jmp +517
acc -6
acc +13
jmp +140
nop +348
acc +0
jmp +275
jmp +52
jmp +110
acc +11
acc +15
jmp +13
acc +7
jmp +216
jmp +174
nop +24
acc -16
acc +46
acc -17
jmp +519
acc -15
acc +46
acc -4
jmp +309
acc +14
acc +36
acc -15
jmp +244
acc +37
acc +43
jmp +146
jmp +260
jmp +217
acc +39
jmp +454
nop +16
nop +255
acc +31
jmp +13
acc +38
acc +45
acc +24
jmp +534
acc +13
acc +44
acc +34
jmp +286
jmp +1
acc -12
jmp -45
jmp +147
acc -2
acc +24
nop +391
acc +11
jmp +242
acc +1
acc +28
jmp +423
acc +5
jmp +319
acc +45
nop +350
acc +34
acc +7
jmp +47
nop +32
acc +2
acc +0
jmp +252
acc -4
acc +23
jmp +452
acc -5
acc +48
jmp -104
acc +38
jmp +172
acc +7
acc +31
jmp +5
acc +19
acc +12
acc +26
jmp +232
acc -12
nop +121
nop +80
acc +46
jmp +126
jmp +82
nop +69
jmp -128
acc +18
acc +45
acc +14
acc +45
jmp +219
jmp +422
acc +2
acc +40
acc +13
jmp +450
acc +48
jmp +172
acc +19
acc -10
jmp +69
nop +336
nop -6
jmp +265
jmp -136
jmp +350
acc +31
acc +39
nop +389
nop +404
jmp +16
acc +13
nop -41
acc -2
acc -14
jmp +159
jmp -111
acc +40
acc +36
acc -17
jmp -143
acc +36
acc +29
acc +19
acc +0
jmp +159
jmp +279
acc +31
jmp +346
acc +15
nop +173
acc +48
jmp -183
acc +16
acc +31
jmp +418
acc -13
jmp +280
acc +30
nop +229
jmp -139
acc +0
acc +9
jmp +354
acc +12
jmp +310
jmp -129
acc -8
jmp -96
acc -3
acc +1
jmp +51
jmp +303
acc +28
jmp -186
acc +36
acc -10
nop +72
nop +345
jmp +200
acc +6
acc -14
jmp +87
nop +318
jmp +273
nop +309
acc +50
jmp +147
jmp +387
acc +38
nop -169
acc +44
jmp +28
nop +208
nop +43
acc +26
acc -13
jmp -160
jmp +233
acc +22
jmp +357
jmp +374
acc -6
acc +38
jmp +100
jmp -36
acc +38
nop +330
acc +46
jmp -43
acc +34
nop +239
acc +45
acc +15
jmp +48
acc +49
acc +20
acc -5
acc +41
jmp +70
jmp +211
jmp +144
acc +29
acc +36
acc -15
jmp -24
jmp +1
jmp -17
acc -18
acc +27
acc +34
jmp -21
jmp +1
acc +35
acc -5
acc +24
jmp +337
nop -240
jmp +180
acc -1
nop +49
jmp +260
acc +40
acc +42
jmp -165
acc +31
acc +30
nop -234
jmp +27
acc +45
acc +48
acc +44
acc -19
jmp +70
acc +20
acc +18
jmp +219
acc +46
jmp -85
acc +43
acc +21
jmp -4
acc +37
acc +26
acc +16
jmp -257
acc +39
acc +7
jmp -260
acc +42
acc +10
acc +36
acc +47
jmp +2
jmp -249
acc +20
acc -1
acc +21
jmp +74
jmp +31
acc +32
jmp +64
acc +34
jmp -255
acc -8
acc -2
acc +26
jmp -102
jmp +229
acc -14
acc +25
jmp -154
acc -15
jmp -92
nop -37
acc -5
acc +50
acc +43
jmp +73
acc +1
acc -17
acc +19
acc +24
jmp -319
nop -225
jmp -304
acc +49
acc +5
acc -17
jmp +14
acc +42
acc -9
acc -10
acc +45
jmp -125
jmp -46
acc +13
acc +11
nop +199
acc -19
jmp -159
acc +1
jmp +253
acc +7
jmp +233
nop -76
acc +31
acc +44
jmp -18
acc +47
nop +227
jmp +178
nop -22
jmp -44
jmp +24
nop +122
acc +20
acc +43
jmp -81
acc -15
acc +10
acc +40
jmp +108
acc +45
jmp +35
acc +44
jmp +36
nop -2
nop -320
jmp +1
acc +47
jmp -6
acc -16
acc +49
nop +56
jmp +104
acc +40
jmp -159
acc +30
jmp +56
acc +47
acc -6
acc +47
acc +2
jmp -102
acc +45
jmp -262
acc +36
acc +42
acc -17
jmp -90
acc +18
nop +7
acc -14
jmp -194
acc +16
acc +31
acc +26
jmp -257
acc +25
jmp -367
jmp +69
nop -102
acc +47
jmp -356
nop -105
acc +6
jmp -42
acc +40
jmp -368
acc +42
jmp +84
acc +17
acc +14
acc -17
acc -14
jmp -80
acc +42
acc +11
acc -14
jmp -77
acc -12
acc +8
acc -19
jmp -206
acc +6
acc +18
nop +94
acc -2
jmp -330
acc -15
jmp -367
acc -15
acc +40
jmp +143
jmp -178
acc -1
jmp +140
acc +13
acc +47
jmp -271
acc +29
nop -30
nop -344
jmp -251
jmp +98
acc +45
acc -17
acc +5
jmp +1
jmp -299
acc +34
acc +7
acc +7
nop +16
jmp -106
jmp -399
jmp -291
acc -4
acc +26
jmp -376
nop -444
nop +59
acc +27
nop +89
jmp -188
acc +21
nop -246
acc +6
jmp -24
acc +35
jmp +1
jmp -361
acc +48
acc -5
acc +19
jmp +74
jmp -56
jmp +43
acc +50
nop -275
acc +39
acc -11
jmp -258
acc +8
jmp -190
acc +46
jmp +1
nop -188
acc -15
jmp +12
nop -5
nop -444
acc +0
jmp -129
acc -11
acc +28
jmp -452
acc -4
acc +24
nop -176
jmp -56
acc +47
acc +33
jmp -432
jmp -19
acc +32
jmp +1
acc +7
nop -179
jmp -49
nop -66
acc +20
jmp -122
acc +1
acc +10
acc +16
jmp +40
acc +11
acc +6
jmp -454
acc -2
acc +12
nop -228
jmp -165
acc +42
nop -212
acc +49
jmp -286
acc +42
acc +24
acc +38
jmp -440
acc +29
acc +8
acc +21
jmp -288
acc +2
jmp -427
acc +17
acc +45
acc +33
jmp -333
acc +6
jmp -445
nop -283
acc -18
jmp +1
jmp +1
jmp -492
jmp +53
acc +26
jmp -107
nop -377
jmp -155
acc +22
jmp -523
jmp -127
acc +2
nop -168
acc +15
jmp -343
acc +34
acc +0
acc +0
jmp -241
acc +30
acc +40
acc +46
acc -11
jmp -216
acc +31
jmp -86
acc +34
acc -15
nop -4
jmp -74
acc -1
acc +13
acc -2
jmp -119
acc +21
nop -516
acc +24
jmp -580
nop -200
acc +18
jmp -318
acc +0
nop -483
acc +15
acc -9
jmp -30
jmp -462
jmp -476
acc +18
acc -14
jmp -91
acc -6
acc +32
nop -611
acc +8
jmp -613
acc +23
acc +7
acc +30
acc +48
jmp -222
jmp -326
acc +46
nop -108
acc +17
acc -16
jmp +1

``````use crate::common::AdventOfCodeDay;

use itertools::Itertools;
use std::collections::HashSet;
use std::fmt::Display;

#[derive(Debug, Clone)]
struct HGCProgramm {
code: Vec<HGCCommand>,
}

impl HGCProgramm {
fn parse_program(codestr: String) -> HGCProgramm {
HGCProgramm {
code: codestr.lines().map(HGCCommand::parse).collect(),
}
}
}

#[derive(Debug, Clone)]
struct HGCCommand {
cmdtype: HGCCommandType,
argument:  i32,
}

impl HGCCommand {
fn parse(line: &str) -> HGCCommand {
let (str_cmd, str_arg) =  line.split(' ').collect_tuple::<(_, _)>().unwrap();
HGCCommand {
cmdtype: HGCCommandType::parse(str_cmd),
argument: str_arg.parse::<i32>().unwrap(),
}
}
}

#[derive(Debug, PartialEq, Clone)]
enum HGCCommandType {
NOP,
ACC,
JMP,
}

impl HGCCommandType {
fn parse(val: &str) -> HGCCommandType {
match val {
"acc" => HGCCommandType::ACC,
"jmp" => HGCCommandType::JMP,
"nop" => HGCCommandType::NOP,
_ => panic!("not a cmd")
}
}
}

impl Display for HGCCommandType {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
write!(f, "{:?}", self)
}
}

#[derive(Debug)]
struct HGCMachineState {
trace: bool,

acc: i32,
ip: usize,
}

impl HGCMachineState {
fn new() -> HGCMachineState {
HGCMachineState {
trace: is_verbose!(),

acc: 0,
ip: 0,
}
}

fn exec_step(&mut self, prog: &HGCProgramm) {
self.exec_single(&prog.code[self.ip])
}

fn exec_single(&mut self, cmd: &HGCCommand) {
if self.trace {
verboseln!("ip: {: <4}  ||  cmd:[{}({: <5})]  (acc: {})", self.ip, cmd.cmdtype, cmd.argument, self.acc)
}

if cmd.cmdtype == HGCCommandType::NOP {
self.ip += 1;
} else if cmd.cmdtype == HGCCommandType::JMP {
self.ip = (self.ip as i32 + cmd.argument) as  usize;
} else if cmd.cmdtype == HGCCommandType::ACC {
self.acc += cmd.argument;
self.ip += 1;
}
}
}

pub struct Day08 {
input: HGCProgramm,
}

impl Day08 {
pub fn new() -> Self {
let input_bytes = include_bytes!("../res/08_input.txt");
let input_str = String::from_utf8_lossy(input_bytes);

Self {
input: HGCProgramm::parse_program(input_str.to_owned().to_string())
}
}

fn find_loop(prog: &HGCProgramm) -> (i32, bool) {
let mut vm = HGCMachineState::new();

let mut visited: HashSet<usize> = HashSet::new();
visited.insert(vm.ip);

loop {
vm.exec_step(prog);
if visited.contains(&vm.ip) {
return (vm.acc, false);
}
visited.insert(vm.ip);

if vm.ip == prog.code.len() {
return (vm.acc, true);
}
}
}
}

return Day08::find_loop(&self.input).0.to_string();
}

for i in 0..self.input.code.len() {
if self.input.code[i].cmdtype == HGCCommandType::ACC {
continue;
}

let mut progclone = self.input.clone();

if self.input.code[i].cmdtype == HGCCommandType::JMP {
progclone.code[i] = HGCCommand {
cmdtype: HGCCommandType::NOP,
argument: self.input.code[i].argument,
}
} else if self.input.code[i].cmdtype == HGCCommandType::NOP {
progclone.code[i] = HGCCommand {
cmdtype: HGCCommandType::JMP,
argument: self.input.code[i].argument,
}
} else {
panic!();
}

if let (acc, true) = Day08::find_loop(&progclone) {
return acc.to_string();
}
}

panic!();
}
}``````
Result Part 1: 1684
Result Part 2: 2188

made with vanilla PHP and MySQL, no frameworks, no bootstrap, no unnecessary* javascript