style(day01): add some comments, minor cleanup

src/day01.rs

@@ -1,54 +1,60 @@
 use lazy_static::lazy_static;
 use regex::Regex;
 
-use crate::utils::digit_value;
-use crate::Day;
+use crate::{utils::digit_value, Day};
 
+// Register this day in our runner inventory
 inventory::submit! {
     Day { number: 1, run }
 }
 
 fn first_and_last_digit(s: &str) -> usize {
+    // Find the first character in the string that is an ASCII digit
     let first = s
         .chars()
-        .find(|c| c.is_ascii_digit())
-        .unwrap()
-        .to_digit(10)
-        .unwrap() as usize;
+        .find(|c| c.is_ascii_digit()) // Use find to get an Option containing the first digit character
+        .unwrap() // Unwrap the Option, panicking if no digit is found
+        .to_digit(10) // Convert the character to a digit in base 10
+        .unwrap() as usize; // Convert the digit to a usize
+
+    // Find the last character in the string that is an ASCII digit
     let last = s
         .chars()
-        .rfind(|c| c.is_ascii_digit())
-        .unwrap()
-        .to_digit(10)
-        .unwrap() as usize;
+        .rfind(|c| c.is_ascii_digit()) // Use rfind to get an Option containing the last digit character
+        .unwrap() // Unwrap the Option, panicking if no digit is found
+        .to_digit(10) // Convert the character to a digit in base 10
+        .unwrap() as usize; // Convert the digit to a usize
 
+    // Return the result
     first * 10 + last
 }
 
-fn day01_part1(input: &str) -> usize {
-    input.lines().map(first_and_last_digit).sum()
-}
-
 lazy_static! {
     static ref REGEX: Regex =
         Regex::new(r"(?P<digit>zero|one|two|three|four|five|six|seven|eight|nine|\d)").unwrap();
 }
 
 fn first_and_last_digit_regex(s: &str) -> usize {
+    // Initialize variables to keep track of the positions and values of the first and last digits.
     let mut first_start = usize::MAX;
     let mut last_end = 0;
     let mut first_digit = String::new();
     let mut last_digit = String::new();
 
+    // Iterate over each character index in the string.
     for (index, _) in s.char_indices() {
+        // Check if there is a digit at the current index or beyond.
         if let Some(mat) = REGEX.find(&s[index..]) {
+            // Calculate the start and end positions of the matched digit.
             let match_start = index + mat.start();
             let match_end = index + mat.end();
 
+            // If the current match starts before any previously found digit, it's the new first digit.
             if match_start < first_start {
                 first_start = match_start;
                 first_digit = mat.as_str().to_string();
             }
+            // If the current match ends after any previously found digit, it's the new last digit.
             if match_end > last_end {
                 last_end = match_end;
                 last_digit = mat.as_str().to_string();
@@ -56,10 +62,12 @@ fn first_and_last_digit_regex(s: &str) -> usize {
         }
     }
 
-    let first_digit_val = digit_value(&first_digit);
-    let last_digit_val = digit_value(&last_digit);
+    // Convert the first and last digit strings to their numeric values and return the result
+    digit_value(&first_digit) * 10 + digit_value(&last_digit)
+}
 
-    first_digit_val * 10 + last_digit_val
+fn day01_part1(input: &str) -> usize {
+    input.lines().map(first_and_last_digit).sum()
 }
 
 fn day01_part2(input: &str) -> usize {