solution: day 3

data/examples/03.txt

@@ -0,0 +1,10 @@
+467..114..
+...*......
+..35..633.
+......#...
+617*......
+.....+.58.
+..592.....
+......755.
+...$.*....
+.664.598..

src/bin/03.rs

@@ -0,0 +1,104 @@
+struct MappedPart {
+    number: u32,
+    line: usize,
+    start: usize,
+    end: usize,
+}
+
+impl MappedPart {
+    fn is_adjacent(&self, line: usize, column: usize) -> bool {
+        self.line.abs_diff(line) <= 1
+            && (self.start.abs_diff(column) <= 1 || self.end.abs_diff(column) <= 1)
+    }
+}
+
+fn build_map(input: &str) -> Vec<MappedPart> {
+    let mut numbers = Vec::new();
+    for (idl, line) in input.lines().enumerate() {
+        let mut index = 0;
+        for n in line.split(|c: char| !c.is_ascii_digit()) {
+            if n.is_empty() {
+                index += 1;
+                continue;
+            }
+
+            let num: u32 = n.parse().unwrap();
+            let num_len = n.len();
+
+            numbers.push(MappedPart {
+                number: num,
+                line: idl,
+                start: index,
+                end: index + num_len - 1,
+            });
+
+            index += num_len + 1;
+        }
+    }
+
+    numbers
+}
+
+pub fn part_one(input: &str) -> Option<u32> {
+    let numbers = build_map(input);
+
+    let mut part_numbers = 0;
+
+    for (idl, line) in input.lines().enumerate() {
+        for (idc, _) in line
+            .chars()
+            .enumerate()
+            .filter(|(_, c)| !(*c == '.' || c.is_ascii_digit()))
+        {
+            part_numbers += numbers
+                .iter()
+                .filter(|mp| mp.is_adjacent(idl, idc))
+                .map(|mp| mp.number)
+                .sum::<u32>();
+        }
+    }
+
+    Some(part_numbers)
+}
+
+pub fn part_two(input: &str) -> Option<u32> {
+    let numbers = build_map(input);
+
+    let mut gear_ratios = 0;
+
+    for (idl, line) in input.lines().enumerate() {
+        for (idc, _) in line.chars().enumerate().filter(|(_, c)| *c == '*') {
+            let touching: Vec<_> = numbers
+                .iter()
+                .filter(|mp| mp.is_adjacent(idl, idc))
+                .map(|mp| mp.number)
+                .collect();
+            if touching.len() == 2 {
+                gear_ratios += touching.iter().product::<u32>();
+            }
+        }
+    }
+
+    Some(gear_ratios)
+}
+
+aoc::solution!(3);
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    #[test]
+    fn test_part_one() {
+        assert_eq!(
+            part_one(&aoc::template::read_file("examples", 3)),
+            Some(4361)
+        );
+    }
+    #[test]
+    fn test_part_two() {
+        assert_eq!(
+            part_two(&aoc::template::read_file("examples", 3)),
+            Some(467835)
+        );
+    }
+}