immortaly007/advent-of-code-2023-rust
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

[TWEAK] Day 6 is now solved with math, making it a lot faster

Browse Source
This commit is contained in:
Bas Dado
2023-12-06 19:15:14 +01:00
parent e2b87340e2
commit 95da8147ec
1 changed files with 13 additions and 8 deletions
Download Patch File Download Diff File Expand all files Collapse all files

21
src/day6.rs
View File

@@ -1,5 +1,5 @@
use num::integer::sqrt;
use num::ToPrimitive; use num::ToPrimitive;
use crate::day_solver::DaySolver; use crate::day_solver::DaySolver;
#[cfg(test)] #[cfg(test)]
use crate::util::read_file; use crate::util::read_file;
@@ -30,13 +30,18 @@ impl Day6 {
fn calc_ways_to_beat(time: u64, dist: u64) -> u64 { fn calc_ways_to_beat(time: u64, dist: u64) -> u64 {
let mut records_this_race = 0u64; // y = (t - x) * x = tx - x^2
for pressed in 0..time { // We need to solve for tx - x^2 = d
if Day6::calc_dist(time, pressed) > dist { // Solve for x:
records_this_race += 1; // x = (t - sqrt(t^2 -4d)) / 2
} // x = (sqrt(t^2 -4d) + t) / 2
} // Difference between those two solutions is the answer
return records_this_race
let time_f = time.to_f64().unwrap();
let dist_f = dist.to_f64().unwrap();
let min_win = (time_f - f64::sqrt(time_f * time_f - 4f64 * dist_f)) / 2f64;
let max_win = (f64::sqrt(time_f * time_f - 4f64 * dist_f) + time_f) / 2f64;
return f64::floor(max_win).to_u64().unwrap() - f64::ceil(min_win).to_u64().unwrap() + 1;
} }
} }