2023: Day 6, part 1

2023/day6/Cargo.lock

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+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "day6"
+version = "0.1.0"

2023/day6/Cargo.toml

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+[package]
+name = "day6"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]

2023/day6/src/main.rs

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+use std::{env, fs};
+
+type BoxError = Box<dyn std::error::Error>;
+
+fn main() -> Result<(), BoxError> {
+    let input_path = env::args_os()
+        .skip(1)
+        .next()
+        .ok_or("missing input file path")?;
+    let input = fs::read_to_string(input_path)?;
+    let mut lines = input.lines();
+    let times = lines.next().ok_or("missing times")?;
+    let distances = lines.next().ok_or("missing distances")?;
+
+    let times = parse("Time:", times)?;
+    let distances = parse("Distance:", distances)?;
+    if times.len() != distances.len() {
+        return Err("time/distance length mismatch".into());
+    }
+
+    let mut results = vec![0; times.len()];
+    for (i, (time, record_distance)) in times
+        .iter()
+        .copied()
+        .zip(distances.iter().copied())
+        .enumerate()
+    {
+        (1..time - 1).for_each(|hold| {
+            let velocity = hold;
+            let distance = (time - hold) * velocity;
+            if distance > record_distance {
+                results[i] += 1;
+            }
+        })
+    }
+
+    println!("Part 1: {}", results.iter().fold(1, |a, b| a * b));
+
+    Ok(())
+}
+
+fn parse(prefix: &str, line: &str) -> Result<Vec<usize>, BoxError> {
+    if !line.starts_with(prefix) {
+        return Err(format!("line did not match expected prefix ({}): {}", prefix, line).into());
+    }
+
+    let numbers = line
+        .split_ascii_whitespace()
+        .skip(1)
+        .filter(|word| !word.is_empty())
+        .map(|word| word.parse::<usize>())
+        .collect::<Result<Vec<_>, _>>()?;
+    Ok(numbers)
+}

2023/input/day6.sample

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

2023/input/day6.txt

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+Time:        60     80     86     76
+Distance:   601   1163   1559   1300