Completed day 9

day09/Cargo.lock

@@ -0,0 +1,14 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+[[package]]
+name = "anyhow"
+version = "1.0.35"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2c0df63cb2955042487fad3aefd2c6e3ae7389ac5dc1beb28921de0b69f779d4"
+
+[[package]]
+name = "day09"
+version = "0.1.0"
+dependencies = [
+ "anyhow",
+]

day09/Cargo.toml

@@ -0,0 +1,10 @@
+[package]
+name = "day09"
+version = "0.1.0"
+authors = ["Tyler Hallada <tyler@hallada.net>"]
+edition = "2018"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+anyhow = "1.0"

day09/input/test.txt

@@ -0,0 +1,20 @@
+35
+20
+15
+25
+47
+40
+62
+55
+65
+95
+102
+117
+150
+182
+127
+219
+299
+277
+309
+576

day09/src/main.rs

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+use std::fs::File;
+use std::io::prelude::*;
+use std::io::BufReader;
+use std::time::Instant;
+
+use anyhow::Result;
+
+const INPUT: &str = "input/input.txt";
+
+fn find_invalid_num(nums: &[usize], preamble: usize) -> Option<usize> {
+    if let Some(num) = nums.windows(preamble + 1).find(|chunk| {
+        for num in &chunk[0..preamble] {
+            for other_num in &chunk[0..preamble] {
+                if num != other_num && num + other_num == chunk[preamble] {
+                    return false;
+                }
+            }
+        }
+        true
+    }) {
+        return Some(num[preamble]);
+    }
+    None
+}
+
+fn find_encryption_weakness(nums: &[usize], invalid_num: usize) -> Option<usize> {
+    let mut window_size = 2;
+    while window_size < 1000 {
+        if let Some(weakness) = nums
+            .windows(window_size)
+            .find(|chunk| chunk.iter().sum::<usize>() == invalid_num)
+        {
+            return Some(
+                weakness.iter().min().expect("non-empty slice")
+                    + weakness.iter().max().expect("non-empty slice"),
+            );
+        } else {
+            window_size += 1;
+        }
+    }
+    None
+}
+
+fn solve_part1(input_path: &str, preamble: usize) -> Result<usize> {
+    let file = File::open(input_path)?;
+    let reader = BufReader::new(file);
+
+    let nums = reader
+        .lines()
+        .map(|line| Ok(line?.parse()?))
+        .collect::<Result<Vec<usize>>>()?;
+    Ok(find_invalid_num(&nums, preamble).unwrap())
+}
+
+fn solve_part2(input_path: &str, invalid_num: usize) -> Result<usize> {
+    let file = File::open(input_path)?;
+    let reader = BufReader::new(file);
+
+    let nums = reader
+        .lines()
+        .map(|line| Ok(line?.parse()?))
+        .collect::<Result<Vec<usize>>>()?;
+    Ok(find_encryption_weakness(&nums, invalid_num).unwrap())
+}
+
+fn main() {
+    let mut now = Instant::now();
+    let part1 = solve_part1(INPUT, 25).unwrap();
+    println!("Part 1: {}", part1);
+    println!(
+        "(elapsed: {} ms)",
+        now.elapsed().as_micros() as f32 / 1000_f32
+    );
+    now = Instant::now();
+    println!("");
+    println!("Part 2: {}", solve_part2(INPUT, part1).unwrap());
+    println!(
+        "(elapsed: {} ms)",
+        now.elapsed().as_micros() as f32 / 1000_f32
+    );
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const TEST_INPUT: &str = "input/test.txt";
+
+    #[test]
+    fn solves_part1() {
+        assert_eq!(solve_part1(TEST_INPUT, 5).unwrap(), 127);
+    }
+
+    #[test]
+    fn solves_part2() {
+        assert_eq!(solve_part2(TEST_INPUT, 127).unwrap(), 62);
+    }
+}