-
Notifications
You must be signed in to change notification settings - Fork 4
/
day23.rs
81 lines (75 loc) · 2.45 KB
/
day23.rs
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
//! # Coprocessor Conflagration
//!
//! Just like [`Day 18`] reverse engineering the code is essential. The entire input can be reduced
//! to only the very first number.
//!
//! ```none
//! set b $NUMBER if a == 0 {
//! set c b b = $NUMBER;
//! jnz a 2 c = b;
//! jnz 1 5 } else {
//! mul b 100 b = 100000 + 100 * $NUMBER;
//! sub b -100000 c = b + 17000;
//! set c b }
//! sub c -17000
//! set f 1 for b in (b..=c).step_by(17) {
//! set d 2 f = 1;
//! set e 2 for d in 2..b {
//! set g d for e in 2..b {
//! mul g e if d * e == b {
//! sub g b f = 0;
//! jnz g 2 }
//! set f 0
//! sub e -1
//! set g e
//! sub g b
//! jnz g -8 }
//! sub d -1
//! set g d
//! sub g b
//! jnz g -13 }
//! jnz f 2
//! sub h -1 if f == 0 {
//! set g b h += 1;
//! sub g c }
//! jnz g 2
//! jnz 1 3
//! sub b -17
//! jnz 1 -23 }
//! ```
//!
//! ## Part One
//!
//! The number of `mul` operations is the product of the two inner loops from 2 to `n` exclusive.
//!
//! ## Part Two
//!
//! Counts the number of composite numbers starting from `100,000 + 100 * n` checking the next
//! 1,000 numbers in steps of 17. The raw code take `O(n²)` complexity for each number so emulating
//! this directly would take at least 10⁵.10⁵.10³ = 10¹³ = 10,000,000,000,000 steps.
//!
//! [`Day 18`]: crate::year2017::day18
use crate::util::math::*;
use crate::util::parse::*;
/// We only need the vrey first number from the input.
pub fn parse(input: &str) -> u32 {
input.unsigned()
}
/// The number of `mul` operations is `(n - 2)²`
pub fn part1(input: &u32) -> u32 {
(input - 2) * (input - 2)
}
/// Count the number of composite numbers in a range calculated from the input number.
pub fn part2(input: &u32) -> usize {
(0..=1000).filter_map(|n| composite(100_000 + 100 * input + 17 * n)).count()
}
/// Simple [prime number check](https://en.wikipedia.org/wiki/Primality_test)
/// of all factors from 2 to √n inclusive.
fn composite(n: u32) -> Option<u32> {
for f in 2..=n.sqrt() {
if n % f == 0 {
return Some(n);
}
}
None
}