Day 6

src/day06.rs

@@ -0,0 +1,80 @@
+pub fn run() {
+    let input = [
+        Race {
+            time: 35,
+            record: 213,
+        },
+        Race {
+            time: 69,
+            record: 1168,
+        },
+        Race {
+            time: 68,
+            record: 1086,
+        },
+        Race {
+            time: 87,
+            record: 1248,
+        },
+    ];
+
+    // example
+    // let input = [
+    //     Race { time: 7, record: 9 },
+    //     Race {
+    //         time: 15,
+    //         record: 40,
+    //     },
+    //     Race {
+    //         time: 30,
+    //         record: 200,
+    //     },
+    // ];
+
+    let product_of_ways_of_beating_races = input
+        .iter()
+        .map(|r| r.count_ways_of_beating_record())
+        .product::<u64>();
+    dbg!(product_of_ways_of_beating_races);
+
+    let input_combined = Race {
+        time: 35696887,
+        record: 213116810861248,
+    };
+    // example
+    // let input_combined = Race {
+    //     time: 71530,
+    //     record: 940200,
+    // };
+    dbg!(input_combined.count_ways_of_beating_record());
+}
+
+#[derive(Debug, Clone, Copy)]
+struct Race {
+    time: u64,
+    record: u64,
+}
+
+impl Race {
+    fn count_ways_of_beating_record(&self) -> u64 {
+        let mut slowest_record_beating_speed = None;
+        for v in 0..self.time {
+            if calculate_distance(self.time, v) > self.record {
+                slowest_record_beating_speed = Some(v);
+                break;
+            }
+        }
+        let mut fastest_record_beating_speed = None;
+        for v in (0..self.time).rev() {
+            if calculate_distance(self.time, v) > self.record {
+                fastest_record_beating_speed = Some(v);
+                break;
+            }
+        }
+        fastest_record_beating_speed.unwrap() - slowest_record_beating_speed.unwrap() + 1
+    }
+}
+
+fn calculate_distance(total_time: u64, hold_time: u64) -> u64 {
+    hold_time * (total_time - hold_time)
+}

src/main.rs

@@ -6,7 +6,8 @@ mod day02;
 mod day03;
 mod day04;
 mod day05;
+mod day06;
 
 fn main() {
-    day05::run();
+    day06::run();
 }