day 1 solution

Cargo.lock

@@ -0,0 +1,16 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "anyhow"
+version = "1.0.51"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8b26702f315f53b6071259e15dd9d64528213b44d61de1ec926eca7715d62203"
+
+[[package]]
+name = "aoc2021"
+version = "0.1.0"
+dependencies = [
+ "anyhow",
+]

Cargo.toml

@@ -6,3 +6,4 @@ edition = "2021"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
+anyhow = "1.0"

data/day01-test.txt

@@ -0,0 +1,10 @@
+199
+200
+208
+210
+200
+207
+240
+269
+260
+263

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(())
 }