Completed: 1, 2, 3, 4, 5.1, 6.1, 7, 8

day_06/Cargo.lock

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+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "autocfg"
+version = "1.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d468802bab17cbc0cc575e9b053f41e72aa36bfa6b7f55e3529ffa43161b97fa"
+
+[[package]]
+name = "day_06"
+version = "0.1.0"
+dependencies = [
+ "num-integer",
+]
+
+[[package]]
+name = "num-integer"
+version = "0.1.45"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "225d3389fb3509a24c93f5c29eb6bde2586b98d9f016636dff58d7c6f7569cd9"
+dependencies = [
+ "autocfg",
+ "num-traits",
+]
+
+[[package]]
+name = "num-traits"
+version = "0.2.17"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "39e3200413f237f41ab11ad6d161bc7239c84dcb631773ccd7de3dfe4b5c267c"
+dependencies = [
+ "autocfg",
+]

day_06/Cargo.toml

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+[package]
+name = "day_06"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+num-integer = "0.1.45"

day_06/input.txt

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+Time:      7  15   30
+Distance:  9  40  200

day_06/rustfmt.toml

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+hard_tabs = true

day_06/src/main.rs

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+use std::fs;
+
+use num_integer::Roots;
+
+fn main() {
+	let data = fs::read_to_string("input.txt").unwrap();
+	let (time_str, record_str) = data.split_once('\n').unwrap();
+	let times: Vec<i64> = time_str
+		.split_whitespace()
+		.skip(1)
+		.map(|t| t.parse().unwrap())
+		.collect();
+	let records: Vec<i64> = record_str
+		.split_whitespace()
+		.skip(1)
+		.map(|t| t.parse().unwrap())
+		.collect();
+	let answer = times
+		.iter()
+		.zip(records.iter())
+		.map(|(&time, &record)| beat(time, record))
+		.fold(1, |a, b| a * b);
+	println!("{answer}");
+
+	let big_time: i64 = time_str[7..].replace(' ', "").parse().unwrap();
+	let big_record: i64 = record_str[9..].trim().replace(' ', "").parse().unwrap();
+
+	/*
+	distance = held * (time - held)
+
+	held * (time - held) = record
+	held*time - held*held = record
+	held*time - held*held - record = 0
+	held*held - held*time + record = 0
+	*/
+	// let lower = ((time * time / 4) - record).sqrt() - time / 2;
+	// let upper = -((time * time / 4) - record).sqrt() - time / 2;
+	// println!("{lower} -> {upper}");
+}
+
+fn beat(time: i64, record: i64) -> i64 {
+	let mut variants = 0;
+	for t in 0..time {
+		let dist = t * (time - t);
+		if dist > record {
+			variants += 1;
+		}
+	}
+
+	let time = time as f64;
+	let record = record as f64;
+	let lower = ((time * time / 4.0) - record).sqrt() - time / 2.0;
+	let upper = -((time * time / 4.0) - record).sqrt() - time / 2.0;
+	println!("{lower} -> {upper}");
+
+	variants
+}