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use nom::{
branch::alt,
bytes::complete::tag,
character::complete::line_ending,
combinator::{map, value},
multi::{many1, separated_list1},
IResult,
};
use std::fs;
fn main() -> Result<(), Box<dyn std::error::Error>> {
let input = fs::read_to_string("inputs/day_25.txt")?;
let parsed = SnafuList::parser(&input).unwrap().1;
dbg!(to_snafu(parsed.sum()));
Ok(())
}
#[derive(Debug, Clone, PartialEq, Eq)]
struct SnafuList(Vec<i64>);
impl SnafuList {
fn parser(input: &str) -> IResult<&str, SnafuList> {
map(
separated_list1(
line_ending,
map(
many1(alt((
value(2, tag("2")),
value(1, tag("1")),
value(0, tag("0")),
value(-1, tag("-")),
value(-2, tag("=")),
))),
|digits| {
let mut result: i64 = 0;
for digit in digits {
result *= 5;
result += digit;
}
result
},
),
),
SnafuList,
)(input)
}
fn sum(&self) -> i64 {
self.0.iter().sum()
}
}
fn to_snafu(mut remaining_value: i64) -> String {
let mut result = String::new();
let mut current_power = 5i64.pow(26);
while current_power > 0 {
let next_digit_range = {
let mut next_digit_power = current_power / 5;
let mut max_next_digit = 0;
while next_digit_power > 0 {
max_next_digit += 2 * next_digit_power;
next_digit_power /= 5;
}
-max_next_digit..=max_next_digit
};
let (digit, digit_value) = [('=', -2), ('-', -1), ('0', 0), ('1', 1), ('2', 2)]
.into_iter()
.filter_map(|(digit, digit_value)| {
let digit_value = digit_value * current_power;
let remaining_if_digit_set = remaining_value - digit_value;
if next_digit_range.contains(&remaining_if_digit_set) {
Some((digit, digit_value))
} else {
None
}
})
.next()
.expect("No digit found");
remaining_value -= digit_value;
result.push(digit);
current_power /= 5;
}
result.trim_start_matches("0").to_owned()
}
#[test]
fn round_trip_works() {
let str_list = vec![
"1=-0-2", "12111", "2=0=", "21", "2=01", "111", "20012", "112", "1=-1=", "1-12", "12",
"1=", "122",
];
let list = SnafuList::parser(&str_list.join("\n")).unwrap().1;
assert_eq!(
list,
SnafuList(vec![
1747, 906, 198, 11, 201, 31, 1257, 32, 353, 107, 7, 3, 37
])
);
for (i, num) in list.0.iter().enumerate() {
assert_eq!(to_snafu(*num), str_list[i]);
}
}
|
