From c15d9534bd29c894a7d89418dd18d6a1c932b38d Mon Sep 17 00:00:00 2001
From: Ty <ty@blahaj.land>
Date: Wed, 6 Dec 2023 06:59:37 -0700
Subject: [PATCH] Quadratics are fun
---
src/day6/mod.rs | 37 +++++++++++++++++++++++--------------
1 file changed, 23 insertions(+), 14 deletions(-)
diff --git a/src/day6/mod.rs b/src/day6/mod.rs
index ff2357a..b4167cd 100644
--- a/src/day6/mod.rs
+++ b/src/day6/mod.rs
@@ -8,7 +8,7 @@ pub struct Day6 {
impl Day for Day6 {
fn part1(&mut self) -> String {
let lines = self.input.lines().map(|l| l.split_ascii_whitespace().skip(1).collect::<Vec<_>>()).collect::<Vec<_>>();
- let races = [
+ let races: [(f64, f64); 4] = [
(lines[0][0].parse().unwrap(), lines[1][0].parse().unwrap()),
(lines[0][1].parse().unwrap(), lines[1][1].parse().unwrap()),
(lines[0][2].parse().unwrap(), lines[1][2].parse().unwrap()),
@@ -18,13 +18,16 @@ impl Day for Day6 {
let mut acc = 1usize;
for (time, record_distance) in races {
- let mut wins = 0usize;
- for time_holding_button in 0..time {
- let distance = (time - time_holding_button) * time_holding_button /* velocity */;
- if distance > record_distance { wins += 1; }
- }
+ // let mut wins = 0usize;
+ // for time_holding_button in 0..time {
+ // let distance = (time - time_holding_button) * time_holding_button /* velocity */;
+ // if distance > record_distance { wins += 1; }
+ // }
+ // Mathy solution:
+ let b = ((time+((time*time-4.0*record_distance).sqrt())) / 2.0).ceil();
+ let a = ((time-((time*time-4.0*record_distance).sqrt())) / 2.0).ceil();
- acc *= wins;
+ acc *= (b - a) as usize;
}
acc.to_string()
@@ -33,13 +36,19 @@ impl Day for Day6 {
fn part2(&mut self) -> String {
let lines = self.input.lines().map(|l| l[10..].split_ascii_whitespace().collect::<String>()).collect::<Vec<_>>();
- let (time, record_distance): (u128, u128) = (lines[0].parse().unwrap(), lines[1].parse().unwrap());
- let mut wins = 0u128;
- for time_holding_button in 0..time {
- let distance = (time - time_holding_button) * time_holding_button /* velocity */;
- if distance > record_distance { wins += 1; }
- }
+ let (time, record_distance): (f64, f64) = (lines[0].parse().unwrap(), lines[1].parse().unwrap());
+ // Boring solution:
+ // let mut wins = 0u128;
+ // for time_holding_button in 0..time {
+ // let distance = (time - time_holding_button) * time_holding_button /* velocity */;
+ // if distance > record_distance { wins += 1; }
+ // }
- wins.to_string()
+ // wins.to_string()
+ // Mathy solution:
+ let b = ((time+((time*time-4.0*record_distance).sqrt())) / 2.0).ceil();
+ let a = ((time-((time*time-4.0*record_distance).sqrt())) / 2.0).ceil();
+
+ (b - a).to_string()
}
}