1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
|
use std::io::{self, Read};
use std::str::FromStr;
#[derive(Clone, Copy)]
enum Operand {
Register(u8),
Immediate(i32),
}
impl FromStr for Operand {
type Err = ();
fn from_str(s: &str) -> Result<Self, ()> {
match s {
"a" => Ok(Operand::Register(0)),
"b" => Ok(Operand::Register(1)),
"c" => Ok(Operand::Register(2)),
"d" => Ok(Operand::Register(3)),
_ => Ok(Operand::Immediate(s.parse().map_err(|_| ())?)),
}
}
}
#[derive(Clone, Copy)]
enum Operation {
Cpy(Operand, Operand),
Inc(Operand),
Dec(Operand),
Jnz(Operand, Operand),
}
impl FromStr for Operation {
type Err = ();
fn from_str(s: &str) -> Result<Self, ()> {
let mut iter = s.split(' ');
match iter.next() {
Some("cpy") => {
let src = iter.next().ok_or(())?.parse()?;
let dest = iter.next().ok_or(())?.parse()?;
Ok(Operation::Cpy(src, dest))
},
Some("inc") => Ok(Operation::Inc(iter.next().ok_or(())?.parse()?)),
Some("dec") => Ok(Operation::Dec(iter.next().ok_or(())?.parse()?)),
Some("jnz") => {
let cond = iter.next().ok_or(())?.parse()?;
let jump = iter.next().ok_or(())?.parse()?;
Ok(Operation::Jnz(cond, jump))
},
_ => Err(()),
}
}
}
#[derive(Default)]
struct Vm {
registers: [i32; 4],
operations: Vec<Operation>,
index: i32,
}
impl FromStr for Vm {
type Err = ();
fn from_str(s: &str) -> Result<Self, ()> {
let mut vm = Self::default();
for line in s.lines() {
vm.operations.push(line.parse()?);
}
Ok(vm)
}
}
impl Vm {
fn step(&mut self) -> bool {
match self.operations[self.index as usize] {
Operation::Cpy(Operand::Immediate(imm), Operand::Register(reg)) => {
self.registers[reg as usize] = imm;
self.index += 1;
},
Operation::Cpy(Operand::Register(src), Operand::Register(dest)) => {
self.registers[dest as usize] = self.registers[src as usize];
self.index += 1;
},
Operation::Inc(Operand::Register(reg)) => {
self.registers[reg as usize] += 1;
self.index += 1;
},
Operation::Dec(Operand::Register(reg)) => {
self.registers[reg as usize] -= 1;
self.index += 1;
},
Operation::Jnz(Operand::Immediate(cond), Operand::Immediate(jump)) => {
if cond != 0 {
self.index += jump;
} else {
self.index += 1;
}
},
Operation::Jnz(Operand::Register(reg), Operand::Immediate(jump)) => {
if self.registers[reg as usize] != 0 {
self.index += jump;
} else {
self.index += 1;
}
},
_ => panic!("invalid operation"),
}
(self.index as usize) < self.operations.len()
}
}
fn solve1(input: &str) -> i32 {
let mut vm: Vm = input.parse().unwrap();
while vm.step() { }
vm.registers[0]
}
fn solve2(input: &str) -> i32 {
let mut vm: Vm = input.parse().unwrap();
vm.registers[2] = 1;
while vm.step() { }
vm.registers[0]
}
fn main() {
let mut input = String::new();
io::stdin().read_to_string(&mut input).unwrap();
println!("Part 1: {}", solve1(&input));
println!("Part 2: {}", solve2(&input));
}
#[test]
fn part1() {
let input = "
cpy 41 a
inc a
inc a
dec a
jnz a 2
dec a
";
assert_eq!(42, solve1(input.trim()));
}
|