day1 -> day01

Cause sorting be that way

day01/src/main.rs

@@ -0,0 +1,67 @@
+use anyhow::{anyhow, Result};
+
+use std::fs::File;
+use std::io::prelude::*;
+use std::io::BufReader;
+
+const INPUT: &str = "input/input.txt";
+
+fn solve_part1(input_path: &str) -> Result<u32> {
+    let file = File::open(input_path)?;
+    let reader = BufReader::new(file);
+
+    let mut prev_lines = Vec::new();
+    for line in reader.lines() {
+        let number: u32 = line?.parse()?;
+        for prev_number in prev_lines.iter() {
+            if number + prev_number == 2020 {
+                return Ok(number * prev_number);
+            }
+        }
+        prev_lines.push(number);
+    }
+
+    Err(anyhow!("Found no pair of numbers that sums to 2020"))
+}
+
+fn solve_part2(input_path: &str) -> Result<u32> {
+    let file = File::open(input_path)?;
+    let reader = BufReader::new(file);
+
+    let mut prev_lines = Vec::new();
+    for line in reader.lines() {
+        let number: u32 = line?.parse()?;
+        for prev_number in prev_lines.iter() {
+            for third_number in prev_lines.iter() {
+                if number + prev_number + third_number == 2020 {
+                    return Ok(number * prev_number * third_number);
+                }
+            }
+        }
+        prev_lines.push(number);
+    }
+
+    Err(anyhow!("Found no three numbers that sum to 2020"))
+}
+
+fn main() {
+    println!("Part 1: {}", solve_part1(INPUT).unwrap());
+    println!("Part 2: {}", solve_part2(INPUT).unwrap());
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const TEST_INPUT: &str = "input/test.txt";
+
+    #[test]
+    fn solves_part1() {
+        assert_eq!(solve_part1(TEST_INPUT).unwrap(), 514579);
+    }
+
+    #[test]
+    fn solves_part2() {
+        assert_eq!(solve_part2(TEST_INPUT).unwrap(), 241861950);
+    }
+}