comments

Author: rene-d

2024/day20/day20.rs

@@ -83,12 +83,21 @@ impl Puzzle {
     fn solve(&self, max_cheats: i32, min_gain: i32) -> u32 {
         let mut nb = 0;
 
+        // to count the cheats, we wiil iterate over all track positions that are
+        // at a Manhattan distance less than the asked one (2 or 20 depending on the part)
+
         for cheat_start in &self.track {
             for cheat_end in &self.track {
-                let dist = cheat_start.manhattan_distance(cheat_end);
+                let cheat_dist = cheat_start.manhattan_distance(cheat_end);
+
+                if cheat_dist <= max_cheats {
+                    // so the distance (or the time in picoseconds) is the sum of the distance
+                    // from the start to the cheat start, the cheat length and the distance from
+                    // the cheat end to the end of the track
+
+                    let time = self.from_start[cheat_start] + cheat_dist + self.to_end[cheat_end];
 
-                if dist <= max_cheats {
-                    let time = self.from_start[cheat_start] + self.to_end[cheat_end] + dist;
+                    // if the gain is sufficient, we count it
                     if time + min_gain <= self.boring {
                         nb += 1;
                     }