day(06): add solution

Signed-off-by: Matej Focko <mfocko@redhat.com>

samples/day06.txt

@@ -0,0 +1,2 @@
+Time:      7  15   30
+Distance:  9  40  200

src/bin/day06.rs

@@ -0,0 +1,80 @@
+use aoc_2023::*;
+
+type Output1 = i32;
+type Output2 = Output1;
+
+#[derive(Debug)]
+struct Race {
+    time: i64,
+    distance: i64,
+}
+
+struct Day06 {
+    races: Vec<Race>,
+}
+impl Solution<Output1, Output2> for Day06 {
+    fn new<P: AsRef<Path>>(pathname: P) -> Self {
+        let lines: Vec<String> = file_to_lines(pathname);
+
+        let times: Vec<i64> = parse_ws_separated(lines[0].split(':').nth(1).unwrap());
+        let distances: Vec<i64> = parse_ws_separated(lines[1].split(':').nth(1).unwrap());
+
+        let races = times
+            .iter()
+            .zip(distances.iter())
+            .map(|(&time, &distance)| Race { time, distance })
+            .collect();
+
+        Self { races }
+    }
+
+    fn part_1(&mut self) -> Output1 {
+        self.races
+            .iter()
+            .map(|r| {
+                (1..r.time)
+                    .filter(|t| (r.time - t) * t > r.distance)
+                    .count() as i32
+            })
+            .product()
+    }
+
+    fn part_2(&mut self) -> Output2 {
+        let merged = self.races.iter().fold(
+            Race {
+                time: 0,
+                distance: 0,
+            },
+            |mut m, r| {
+                let mut t = r.time;
+                let mut d = r.distance;
+
+                while t > 0 {
+                    m.time *= 10;
+                    t /= 10;
+                }
+
+                while d > 0 {
+                    m.distance *= 10;
+                    d /= 10;
+                }
+
+                m.time += r.time;
+                m.distance += r.distance;
+
+                m
+            },
+        );
+
+        (1..merged.time)
+            .filter(|t| (merged.time - t) * t > merged.distance)
+            .count() as i32
+    }
+}
+
+fn main() -> Result<()> {
+    // Day06::run("sample")
+    Day06::main()
+}
+
+test_sample!(day_06, Day06, 288, 71503);