day03 task 1 very functional

src/tasks/day03.rs

@@ -33,32 +33,42 @@ fn visited_points(p: &Vec<&str>) -> HashSet<(i32, i32)> {
             (direction, number)
         })
         .scan((0, 0), |(cx, cy), (direction, number)| {
-            let sx = *cx;
-            let sy = *cy;
-            let mut tx = *cx;
-            let mut ty = *cy;
-            let iter: Box<dyn Iterator<Item = (i32, i32)>> = match direction {
-                'U' => {
-                    ty += number;
-                    Box::new((*cy + 1..=ty).map(move |y| (sx, y)))
+            fn fi(i: i32) -> i32 {
+                i + 1
             }
-                'D' => {
-                    ty -= number;
-                    Box::new((ty..*cy).map(move |y| (sx, y)))
+            fn fd(i: i32) -> i32 {
+                i - 1
             }
-                'R' => {
-                    tx += number;
-                    Box::new((*cx + 1..=tx).map(move |x| (x, sy)))
-                }
-                'L' => {
-                    tx -= number;
-                    Box::new((tx..*cx).map(move |x| (x, sy)))
-                }
-                _ => panic!("unknown direction {}", direction),
+            let fstep = match direction {
+                'U' | 'R' => fi,
+                'D' | 'L' => fd,
+                _ => panic!("Unexpected input"),
             };
-            *cx = tx;
-            *cy = ty;
-            Some(iter)
+            fn fx(point: (i32, i32), f: fn(i32) -> i32) -> (i32, i32) {
+                let (x, y) = point;
+                (f(x), y)
+            }
+            fn fy(point: (i32, i32), f: fn(i32) -> i32) -> (i32, i32) {
+                let (x, y) = point;
+                (x, f(y))
+            }
+            let faxis = match direction {
+                'U' | 'D' => fy,
+                'R' | 'L' => fx,
+                _ => panic!("Unexpected input"),
+            };
+            let steps = (0..number)
+                .scan((*cx, *cy), |(sx, sy), _| {
+                    let (newx, newy) = faxis((*sx, *sy), fstep);
+                    *sx = newx;
+                    *sy = newy;
+                    Some((newx, newy))
+                })
+                .collect::<Vec<(i32, i32)>>();
+            let last = steps.iter().last().unwrap();
+            *cx = last.0;
+            *cy = last.1;
+            Some(steps)
         })
         .flatten()
         .collect()