🐶

VERSION

@@ -1 +1 @@
-⛵
+🐶

y2023/p16.py

@@ -0,0 +1,40 @@
+def reflect(pos, dirx):
+    match '-' if dirx.real else '|', graph.get(pos, ' '):
+        case [_, ' ']: return []
+        case [_, '.']: return [0]
+        case ['-', '-']: return [0]
+        case ['-', 'L']: return [1]
+        case ['-', '/']: return [-1]
+        case ['-', '|']: return [1, -1]
+        case ['|', '|']: return [0]
+        case ['|', '/']: return [1]
+        case ['|', 'L']: return [-1]
+        case ['|', '-']: return [1, -1]
+        case other: raise RuntimeError(other)
+
+
+def solve(start):
+    seen = set()
+    state = {start}
+    while state:
+        seen |= state
+        state = {(pp + dd * 1j ** rr, dd * 1j ** rr) for pp, dd in state for rr in reflect(pp, dd)} - seen
+    return len({x for x, y in seen} & set(graph))
+
+
+text = open(0).read().replace('\\', 'L')
+graph = {
+    complex(x, y): val
+    for y, row in enumerate(text.splitlines())
+    for x, val in enumerate(row)
+}
+print(solve((0, 1)))
+
+xmin, *_, xmax = sorted(int(p.real) for p in graph)
+ymin, *_, ymax = sorted(int(p.imag) for p in graph)
+starts = []
+starts += [(complex(x, ymin), 1j) for x in range(xmin, xmax + 1)]
+starts += [(complex(x, ymax),-1j) for x in range(xmin, xmax + 1)]
+starts += [(complex(xmin, y), 1 ) for y in range(ymin, ymax + 1)]
+starts += [(complex(xmax, y),-1 ) for y in range(ymin, ymax + 1)]
+print(max(solve(start) for start in starts))