day 10, simple grid walk, refactor into lib

lib/grid.py

@@ -0,0 +1,35 @@
+from typing import Any
+from typing import Optional
+
+"""
+same convention as SVG
+           W
+(0,0)┌───────────► x
+     │                
+  H  │                
+     │                
+     │                
+     ▼                
+     y
+grid G store list of rows
+to get G(x,y), must first extract row y and then col y => G[y][x]
+"""
+
+def grid_geom(G:list[list[Any]]) -> tuple[int,int]:
+    H = len(G)
+    W = len(G[0])
+    return W, H
+
+def in_grid(G:list[list[Any]], x:int, y:int) -> bool:
+    W, H = grid_geom(G)
+    return x>=0 and x<W and y>=0 and y<H
+
+def get_in_grid(G:list[list[Any]], x:int, y:int) -> Optional[Any]:
+    if in_grid(G, x,y):
+        return G[y][x]
+
+UP = (0,-1) ; RIGHT = (1,0) ; DOWN = (0,1) ; LEFT = (-1,0)
+
+MOVE4 = [ UP, RIGHT, DOWN, LEFT ]
+DIAG4 = [(1,1),(-1,-1),(1,-1),(-1,1)]
+MOVE8 = MOVE4 + DIAG4