day 10, simple grid walk, refactor into lib

d10/run.py

@@ -0,0 +1,23 @@
+import sys
+from grid import *
+
+L = sys.stdin.read().strip().split("\n")
+G = [list(map(int,l)) for l in L]
+
+def walk(grid, x, y, p=-1):
+    v = get_in_grid(G, x, y)
+    if v is None or v != p + 1: # wrong way
+        return
+    if v == 9:  # end of trail
+        yield (x, y)
+    for dx, dy in MOVE4:
+        yield from walk(grid, x+dx, y+dy, p+1)
+
+U = R = 0
+for (x0,y0) in ((x,y) for y,row in enumerate(G) for x,v in enumerate(row) if v == 0):
+    s = set()
+    for ends in walk(G, x0, y0):
+        s.add(ends)
+        R += 1
+    U += len(s)
+print(U, R)

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