day 1 solution

src/main.rs

@@ -1,3 +1,41 @@
-fn main() {
-    println!("Hello, world!");
+use anyhow::Result;
+use std::fs;
+
+fn read_i64s(filename: &str) -> Result<Vec<i64>> {
+    Ok(read_file(filename)?
+        .lines()
+        .map(|s| s.parse::<i64>().expect("i64 parse error"))
+        .collect())
+}
+
+fn read_file(filename: &str) -> Result<String> {
+    Ok(fs::read_to_string(filename)?)
+}
+
+fn count_incrementing_windows(window: usize, v: &[i64]) -> usize {
+    // create an array of the window sums and then window(2) that array to count increments
+    v.windows(window)
+        .map(|w| w.iter().sum())
+        .collect::<Vec<i64>>()
+        .windows(2)
+        .filter(|s| s[1] > s[0])
+        .count()
+}
+
+fn day01() -> Result<(usize, usize)> {
+    let data = read_i64s("data/day01-test.txt")?;
+    assert_eq!(count_incrementing_windows(1, &data), 7);
+    assert_eq!(count_incrementing_windows(3, &data), 5);
+
+    let data = read_i64s("data/day01.txt")?;
+    let part1 = count_incrementing_windows(1, &data);
+    let part2 = count_incrementing_windows(3, &data);
+    assert_eq!(part1, 1298);
+    assert_eq!(part2, 1248);
+    Ok((part1, part2))
+}
+
+fn main() -> Result<()> {
+    println!("day01: {:?}", day01()?);
+    Ok(())
 }