feat(day6): day6 solution

Cargo.toml

@@ -26,4 +26,8 @@ path = "src/day4/main.rs"
 
 [[bin]]
 name = "day5"
-path = "src/day5/main.rs"
+path = "src/day5/main.rs"
+
+[[bin]]
+name = "day6"
+path = "src/day6/main.rs"

src/day6/example.txt

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

src/day6/main.rs

@@ -0,0 +1,61 @@
+use adventofcode2023::utils::get_puzzle_bytes;
+
+fn parse_line(line: &[u8]) -> Vec<u64> {
+    line.split(|&c| c == b' ')
+        .skip(1)
+        .filter(|b| !b.is_empty())
+        .map(|b| atoi::atoi(b).unwrap())
+        .collect::<Vec<u64>>()
+}
+
+fn compute_ways(time: u64, dist: u64) -> u64 {
+	// first solutiom of quadratic equation
+	// approximation of minimum time to travel the distance
+    let x1 = (time - f32::sqrt((time * time - 4 * dist) as f32) as u64) / 2;
+	// second solutiom of quadratic equation
+	// approximation of maximum time to travel the distance
+    let x2 = time - x1;
+	// longuest distance traveled approximation compared to the real distance for correction
+	// is the result include of exclude the min/max bounds
+    let c = (x2 * x1 <= dist) as u64;
+    x2 - x1 - c * 2 + 1
+}
+
+fn count_ways_to_beat_records(puzzle: &[u8]) -> u64 {
+    let (first_line, second_line) =
+        puzzle.split_at(puzzle.iter().position(|&c| c == b'\n').unwrap());
+    let race_times = parse_line(first_line);
+    let race_distances = parse_line(second_line);
+    race_times
+        .into_iter()
+        .zip(race_distances)
+        .map(|(time, dist)| compute_ways(time, dist))
+        .product()
+}
+
+fn parse_line_part_2(line: &[u8]) -> u64 {
+    line.iter()
+        .filter(|b| b.is_ascii_digit())
+        .fold(0, |acc, b| acc * 10 + (*b - b'0') as u64)
+}
+
+fn count_ways_to_beat_record_part2(puzzle: &[u8]) -> u64 {
+    let (first_line, second_line) =
+        puzzle.split_at(puzzle.iter().position(|&c| c == b'\n').unwrap());
+    let time = parse_line_part_2(first_line);
+    let dist = parse_line_part_2(second_line);
+    compute_ways(time, dist)
+}
+
+fn main() {
+    let puzzle = get_puzzle_bytes();
+    let start_time = std::time::Instant::now();
+    println!("--- Day 6: Wait For It ---");
+    println!("What do you get if you multiply these numbers together?");
+    println!("{}", count_ways_to_beat_records(&puzzle));
+    println!("--- Part Two ---");
+    println!("How many ways can you beat the record in this one much longer race?");
+    println!("{}", count_ways_to_beat_record_part2(&puzzle));
+    let elapsed_time = start_time.elapsed();
+    println!("compute time: {:?}", elapsed_time);
+}

src/day6/puzzle6.txt

@@ -0,0 +1,2 @@
+Time:        51     92     68     90
+Distance:   222   2031   1126   1225