day 10, part 1 ok, part 2 with help, but nice drawing

d10/run.py

@@ -0,0 +1,59 @@
+import sys
+
+# parse
+I = sys.stdin.read().splitlines()
+G = [list(l) for l in I]
+W = len(G[0])
+H = len(G)
+
+# look for S
+S = None
+for y in range(H):
+    if (x := I[y].find("S")) > -1:
+        S = (x,y)
+        break
+
+# encode moves
+D = {
+    'u': {'|': ( 0,-1,'u'), 'F': ( 1, 0,'r'), '7': (-1, 0,'l')},
+    'r': {'-': ( 1, 0,'r'), 'J': ( 0,-1,'u'), '7': ( 0, 1,'d')},
+    'd': {'|': ( 0, 1,'d'), 'L': ( 1, 0,'r'), 'J': (-1, 0,'l')},
+    'l': {'-': (-1, 0,'l'), 'L': ( 0,-1,'u'), 'F': ( 0, 1,'d')},
+}
+
+# part 1
+poly = [S]  # vertices of the polygone
+x0, y0 = S
+P = (x0+1, y0, 'r')  # start at S and go right
+for _ in range(100_000):
+    x, y, d = P
+    poly.append((x,y))
+    z = G[y][x]
+    if z == 'S':
+        break
+    dx,dy,nd = D[d].get(z)
+    P = (x+dx,y+dy,nd)
+print(len(poly)//2)
+
+# part 2
+from matplotlib.path import Path
+
+pg = Path(poly)
+
+J = [['.']*W for _ in range(H)]
+R = 0
+for y in range(W):
+    for x in range(H):
+        if (x,y) in poly:
+            J[y][x] = G[y][x]
+        elif pg.contains_point((x,y)):
+            R += 1
+            J[y][x] = "O"
+print(R)
+
+# plot
+J[y0][x0] = "S"
+T = str.maketrans("|-LJ7F", "│─└┘┐┌")
+with open("grid.txt","wt") as f:
+    for row in J:
+        print("".join(row).translate(T), file=f)