day 1

a-trebuchet/Cargo.lock

@@ -0,0 +1,7 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "a-trebuchet"
+version = "0.1.0"

a-trebuchet/Cargo.toml

@@ -0,0 +1,8 @@
+[package]
+name = "a-trebuchet"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]

a-trebuchet/src/main.rs

@@ -0,0 +1,70 @@
+use std::char;
+
+static INPUT: &str = include_str!("input");
+
+fn main() {
+    println!("part 1's result is: {:?}", part1());
+    println!("part 2's result is: {:?}", part2());
+}
+
+fn part1() -> usize {
+    sum_them_up(INPUT.lines())
+}
+
+fn sum_them_up(input: impl Iterator<Item = impl AsRef<str>>) -> usize {
+    input
+        .map(|line| {
+            let d1 = line
+                .as_ref()
+                .chars()
+                .find(|c| c.is_ascii_digit())
+                .expect("every line has at least one digit");
+            let d2 = line
+                .as_ref()
+                .chars()
+                .rev()
+                .find(|c| c.is_ascii_digit())
+                .expect("every line still has at least one digit");
+            format!("{}{}", d1, d2)
+                .parse::<usize>()
+                .expect("two digits should be parsable as int")
+        })
+        .sum()
+}
+
+static CHECK_MAP: [(&str, char); 9] = [
+    ("one", '1'),
+    ("two", '2'),
+    ("three", '3'),
+    ("four", '4'),
+    ("five", '5'),
+    ("six", '6'),
+    ("seven", '7'),
+    ("eight", '8'),
+    ("nine", '9'),
+];
+
+fn extract_digits(line: &str) -> String {
+    let mut buf = String::new();
+    let mut out = String::new();
+
+    for c in line.chars() {
+        if c.is_ascii_digit() {
+            out.push(c);
+        } else {
+            buf.push(c);
+            if let Some(digit) = CHECK_MAP
+                .into_iter()
+                .find_map(|(pat, dig)| Some(dig).filter(|_| buf.ends_with(pat)))
+            {
+                out.push(digit);
+            }
+        }
+    }
+
+    out
+}
+
+fn part2() -> usize {
+    sum_them_up(INPUT.lines().map(extract_digits))
+}