2020: day01: part 1

aoc2020/src/day01.rs

@@ -0,0 +1,56 @@
+use std::fmt::Write;
+
+use aoc::{err, Result};
+
+const INPUT: &str = include_str!("../input/day01.txt");
+
+pub fn run() -> Result<String> {
+    let mut res = String::with_capacity(128);
+
+    writeln!(res, "part 1: {}", part1(INPUT)?)?;
+
+    Ok(res)
+}
+
+fn part1(input: &str) -> Result<u64> {
+    let entries = input
+        .lines()
+        .map(|line| line.parse::<u64>().map_err(|e| err!("{}", e)))
+        .collect::<Result<Vec<u64>>>()?;
+
+    let (a, b) = find_2020_sum(&entries)?;
+
+    Ok(a * b)
+}
+
+fn find_2020_sum(entries: &[u64]) -> Result<(u64, u64)> {
+    for i in 0..(entries.len()) {
+        for j in 0..entries.len() {
+            if i == j {
+                continue;
+            }
+            if entries[i] + entries[j] == 2020 {
+                return Ok((entries[i], entries[j]));
+            }
+        }
+    }
+
+    Err(err!("couldn't find 2 elements that sum to 2020"))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn part1_provided() {
+        let (a, b) = find_2020_sum(&vec![1721, 979, 366, 299, 675, 1456]).unwrap();
+        assert_eq!(a, 1721);
+        assert_eq!(b, 299);
+    }
+
+    #[test]
+    fn part1_real() {
+        assert_eq!(part1(INPUT).unwrap(), 1014171);
+    }
+}

aoc2020/src/lib.rs

@@ -0,0 +1 @@
+pub mod day01;

aoc2020/src/main.rs

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+use aoc::DayFunc;
+use aoc::Result;
+
+use aoc2020::day01;
+
+fn main() -> Result<()> {
+    let days: &[DayFunc] = &[day01::run];
+
+    aoc::run(days)
+}