Made solution for day 6 faster

crates/solutions/src/day6.rs

@@ -1,3 +1,5 @@
+use std::usize;
+
 mod parsing;
 mod race_record;
 
@@ -16,11 +18,34 @@ pub fn solve_task_1(input: &str) -> String {
 }
 pub fn solve_task_2(input: &str) -> String {
     let parsed = parsing::parsing_part_2(input);
-    let how_many_times_won = all_rounds_of_durations(parsed.time())
+
+    let time_to_beat = parsed.time();
+    assert!(time_to_beat > 1, "Race time must be at least 2");
+    const FIRST_AND_LAST_CYCLE_DO_NOT_MOVE: NumericValue = 2;
+    const HALF_AT_OR_OVER_PEAK: NumericValue = 2;
+    let range: NumericValue =
+        (parsed.time() - FIRST_AND_LAST_CYCLE_DO_NOT_MOVE) / HALF_AT_OR_OVER_PEAK;
+
+    const FIRST_CYCLE_NO_DISTANCE: usize = 1;
+    for (index, next_distance) in all_rounds_of_durations(parsed.time())
         .into_iter()
-        .filter(|&distance| distance > parsed.reached_distance())
+        .enumerate()
-        .count() as NumericValue;
+        .skip(FIRST_CYCLE_NO_DISTANCE)
-    how_many_times_won.to_string()
+    {
+        if next_distance > parsed.reached_distance() {
+            const EVEN_TIME_TO_BEAT_LEADS_UNEVEN_PICK: NumericValue = 1;
+            let one_offset = if time_to_beat % 2 == 0 {
+                EVEN_TIME_TO_BEAT_LEADS_UNEVEN_PICK
+            } else {
+                0
+            };
+            let lower_than_distance_over_pick = (index as NumericValue) - 1;
+            let both_halves = (range - lower_than_distance_over_pick) * 2;
+            let how_many_times_won = both_halves + one_offset;
+            return how_many_times_won.to_string();
+        }
+    }
+    unreachable!();
 }
 
 fn all_rounds_of_durations(duration: NumericValue) -> Vec<NumericValue> {