1 files changed, 37 insertions, 0 deletions
diff --git a/src/bin/day1.rs b/src/bin/day1.rs
new file mode 100644
index 0000000..4784496
--- /dev/null
+++ b/src/bin/day1.rs
@@ -0,0 +1,37 @@
+static DAY: u8 = 1;
+
+fn main() {
+    let input = advent::read_lines(DAY);
+    println!("{DAY}a: {}", sum_digits(&input));
+    println!("{DAY}b: {}", 0);
+}
+
+fn sum_digits(input: &[String]) -> u32 {
+    let mut sum = 0;
+    for line in input {
+        let left_pos = line.find(|c: char| c.is_digit(10)).expect("line contains digit");
+        let right_pos = line.rfind(|c: char| c.is_digit(10)).expect("line contains digit");
+
+        let line = line.as_bytes();
+        let left_digit = (line[left_pos] as char).to_digit(10).unwrap();
+        let right_digit = (line[right_pos] as char).to_digit(10).unwrap();
+        sum += (left_digit * 10 + right_digit) as u32;
+    }
+    sum
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test() {
+        let input = [
+            "1abc2",
+            "pqr3stu8vwx",
+            "a1b2c3d4e5f",
+            "treb7uchet",
+        ].iter().map(|&x| String::from(x)).collect::<Vec<_>>();
+        assert_eq!(sum_digits(&input), 142);
+    }
+}