Naive solution

This commit is contained in:
Tristan Daniël Maat 2020-12-13 22:26:46 +00:00
parent 7b7e983e9a
commit 45ab053ef4
Signed by: tlater
GPG key ID: 49670FD774E43268
4 changed files with 271 additions and 0 deletions
day-13/src

181
day-13/src/main.rs Normal file
View file

@ -0,0 +1,181 @@
use std::fs;
fn main() -> Result<(), Box<dyn std::error::Error>> {
let input = fs::read_to_string("input")?;
let (time, ids) = parse_notes(&input)?;
// Part 1
let (earliest, arrival) = find_closest_bus(time, &ids);
println!("{}", (arrival - time) * earliest);
// Part 2
let timestamp = find_incrementing(&ids);
println!("{}", timestamp);
Ok(())
}
fn parse_notes(input: &str) -> Result<(u32, Vec<u32>), &str> {
let mut lines = input.lines();
let estimate = lines
.next()
.ok_or("Input too short")?
.parse()
.map_err(|_| "Estimate is not a number")?;
let ids = lines
.next()
.ok_or("Input too short")?
.split(',')
.map(|id| id.parse().unwrap_or(0))
.collect();
Ok((estimate, ids))
}
fn find_closest_bus(time: u32, ids: &Vec<u32>) -> (u32, u32) {
ids.iter()
.filter(|id| **id != 0)
.map(|id| {
let mut arrival = *id;
while arrival < time {
arrival += id
}
(*id, arrival)
})
.min_by_key(|id| id.1)
.expect("Must have at least one bus ID")
}
fn find_incrementing(ids: &Vec<u32>) -> u128 {
let ids: Vec<u128> = ids.iter().map(|id| *id as u128).collect();
let (largest, increment) = ids
.iter()
.enumerate()
.max_by_key(|id| id.1)
.expect("Must have at least one bus ID");
let mut iterations = (14166999999493 - largest as u128) / increment;
loop {
iterations += 1;
let max = increment * iterations;
if ids.iter().enumerate().rev().all(|(i, number)| {
if *number == 0 {
true
} else {
let target = max - largest as u128 + i as u128;
target % number == 0
}
}) {
break max - largest as u128;
} else {
if iterations % 100000000 == 0 {
let fun = ids
.iter()
.enumerate()
.filter(|(i, number)| {
if **number == 0 {
true
} else {
let target = max - largest as u128 + *i as u128;
target % **number == 0
}
})
.count();
println!("{} - {}/{}", max - largest as u128, fun, ids.len());
}
}
}
}
#[cfg(test)]
mod tests {
use super::*;
use indoc::indoc;
#[test]
fn test_simple() -> Result<(), Box<dyn std::error::Error>> {
let input = indoc!(
"939
7,13,x,x,59,x,31,19
"
);
let (time, ids) = parse_notes(input)?;
let (earliest, arrival) = find_closest_bus(time, &ids);
assert_eq!(arrival, 944);
Ok(())
}
#[test]
fn test_simple2() -> Result<(), Box<dyn std::error::Error>> {
let input = indoc!(
"939
17,x,13,19
"
);
let (time, ids) = parse_notes(input)?;
let timestamp = find_incrementing(&ids);
assert_eq!(timestamp, 3417);
Ok(())
}
#[test]
fn test_simple3() -> Result<(), Box<dyn std::error::Error>> {
let input = indoc!(
"939
7,13,x,x,59,x,31,19
"
);
let (time, ids) = parse_notes(input)?;
let timestamp = find_incrementing(&ids);
assert_eq!(timestamp, 1068781);
Ok(())
}
#[test]
fn test_simple4() -> Result<(), Box<dyn std::error::Error>> {
let input = indoc!(
"939
67,7,59,61
"
);
let (time, ids) = parse_notes(input)?;
let timestamp = find_incrementing(&ids);
assert_eq!(timestamp, 754018);
Ok(())
}
#[test]
fn test_simple5() -> Result<(), Box<dyn std::error::Error>> {
let input = indoc!(
"939
67,x,7,59,61
"
);
let (time, ids) = parse_notes(input)?;
let timestamp = find_incrementing(&ids);
assert_eq!(timestamp, 779210);
Ok(())
}
}