1 files changed, 103 insertions, 0 deletions
diff --git a/src/day_01.rs b/src/day_01.rs
new file mode 100644
index 0000000..9c0310e
--- /dev/null
+++ b/src/day_01.rs
@@ -0,0 +1,103 @@
+use anyhow::Context;
+
+use crate::{Problem, Solution};
+
+pub struct Day01;
+
+impl Problem for Day01 {
+    const DAY: u8 = 1;
+
+    const INPUT: &'static str = include_str!("../input/day_01.txt");
+}
+
+impl Solution for Day01 {
+    type Answer1 = usize;
+
+    type Answer2 = usize;
+
+    fn part_1(input: &str) -> anyhow::Result<Self::Answer1> {
+        input.trim().split('\n').try_fold(0, |acc, line| {
+            let first = line
+                .chars()
+                .find_map(|c| c.to_digit(10).map(|n| n as usize))
+                .context("Failed to find first number")?;
+
+            let last = line
+                .chars()
+                .rev()
+                .find_map(|c| c.to_digit(10).map(|n| n as usize))
+                .unwrap_or(first);
+
+            Ok(acc + first * 10 + last)
+        })
+    }
+
+    fn part_2(input: &str) -> anyhow::Result<Self::Answer2> {
+        let words = [
+            "zero", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine",
+        ];
+
+        input.trim().split('\n').try_fold(0, |acc, line| {
+            let mut buf = String::new();
+            let first = line
+                .chars()
+                .find_map(|c| {
+                    buf.push(c);
+                    words
+                        .iter()
+                        .enumerate()
+                        .find_map(|(n, w)| buf.contains(w).then_some(n))
+                        .or_else(|| c.to_digit(10).map(|n| n as usize))
+                })
+                .context("Failed to find first number")?;
+
+            buf.clear();
+            let last = line
+                .chars()
+                .rev()
+                .find_map(|c| {
+                    buf.insert(0, c);
+                    words
+                        .iter()
+                        .enumerate()
+                        .find_map(|(n, w)| buf.contains(w).then_some(n))
+                        .or_else(|| c.to_digit(10).map(|n| n as usize))
+                })
+                .unwrap_or(first);
+
+            Ok(acc + first * 10 + last)
+        })
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_part_1() -> anyhow::Result<()> {
+        let input = indoc::indoc! {"
+            1abc2
+            pqr3stu8vwx
+            a1b2c3d4e5f
+            treb7uchet
+        "};
+
+        Ok(assert_eq!(142, Day01::part_1(input)?))
+    }
+
+    #[test]
+    fn test_part_2() -> anyhow::Result<()> {
+        let input = indoc::indoc! {"
+            two1nine
+            eightwothree
+            abcone2threexyz
+            xtwone3four
+            4nineeightseven2
+            zoneight234
+            7pqrstsixteen
+        "};
+
+        Ok(assert_eq!(281, Day01::part_2(input)?))
+    }
+}