feat: solve day 3

data/examples/03.txt

@@ -0,0 +1,5 @@
+987654321111111
+811111111111119
+234234234234278
+818181911112111
+

src/bin/03.rs

@@ -0,0 +1,93 @@
+use std::cmp::Ordering;
+
+use itertools::Itertools;
+
+advent_of_code::solution!(3);
+
+pub fn part_one(input: &str) -> Option<u64> {
+    input
+        .lines()
+        .filter(|line| !line.is_empty())
+        .map(|line| {
+            let first = line
+                .chars()
+                .enumerate()
+                .filter(|c| c.0 != line.len() - 1)
+                .max_by(|a, b| {
+                    if a.1.cmp(&b.1) == Ordering::Equal {
+                        b.0.cmp(&a.0)
+                    } else {
+                        a.1.cmp(&b.1)
+                    }
+                })
+                .unwrap();
+            let second = line
+                .chars()
+                .enumerate()
+                .skip(first.0 + 1)
+                .max_by(|a, b| {
+                    if a.1.cmp(&b.1) == Ordering::Equal {
+                        b.0.cmp(&a.0)
+                    } else {
+                        a.1.cmp(&b.1)
+                    }
+                })
+                .unwrap();
+
+            format!("{}{}", first.1, second.1)
+        })
+        .map(|num_str| num_str.parse().unwrap_or(0))
+        .sum1()
+}
+
+pub fn part_two(input: &str) -> Option<u64> {
+    input
+        .lines()
+        .filter(|line| !line.is_empty())
+        .map(|line| {
+            let mut num_str = vec![];
+            let mut prev = (0, '0');
+            for i in 0..12 {
+                let skip_amt = if i == 0 { 0 } else { prev.0 + 1 };
+                let curr = line
+                    .chars()
+                    .enumerate()
+                    .filter(|c| c.0 <= line.len() - (12 - i))
+                    .skip(skip_amt)
+                    .max_by(|a, b| {
+                        if a.1.cmp(&b.1) == Ordering::Equal {
+                            b.0.cmp(&a.0)
+                        } else {
+                            a.1.cmp(&b.1)
+                        }
+                    })
+                    .unwrap();
+                num_str.push(curr.1);
+                prev = curr;
+            }
+
+            num_str.into_iter().join("")
+        })
+        .map(|num_str| num_str.parse().unwrap_or(0))
+        .sum1()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_part_one() {
+        let mut result = part_one(&advent_of_code::template::read_file("examples", DAY));
+        assert_eq!(result, Some(357));
+
+        result = part_one("622262224226");
+        assert_eq!(result, Some(66));
+    }
+
+    #[test]
+    fn test_part_two() {
+        let result = part_two(&advent_of_code::template::read_file("examples", DAY));
+        assert_eq!(result, Some(3121910778619));
+    }
+}