Solve day 21

2024/21_keypad.py

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+#!/usr/bin/env python3
+import sys
+from functools import cache
+from itertools import pairwise
+
+NUMERIC = '789', '456', '123', ' 0A'
+DIRECTIONAL = ' ^A', '<v>'
+
+def walk(keypad, x, y, path):
+    for direction in path:
+        neighbors = (x - 1, y), (x + 1, y), (x, y - 1), (x, y + 1)
+        x, y = neighbors['<>^v'.index(direction)]
+        yield keypad[y][x]
+
+def paths_between(keypad, start, end):
+    x1, y1 = next((x, y) for y, row in enumerate(keypad)
+                         for x, key in enumerate(row) if key == start)
+    x2, y2 = next((x, y) for y, row in enumerate(keypad)
+                         for x, key in enumerate(row) if key == end)
+    hor = '<>'[x2 > x1] * abs(x2 - x1)
+    ver = '^v'[y2 > y1] * abs(y2 - y1)
+    return tuple(path + 'A' for path in {hor + ver, ver + hor}
+                 if ' ' not in walk(keypad, x1, y1, path))
+
+@cache
+def cost_between(keypad, start, end, links):
+    return min(cost(DIRECTIONAL, path, links - 1)
+               for path in paths_between(keypad, start, end)) if links else 1
+
+@cache
+def cost(keypad, keys, links):
+    return sum(cost_between(keypad, a, b, links)
+               for a, b in pairwise('A' + keys))
+
+def complexity(code, robots):
+    return cost(NUMERIC, code, robots + 1) * int(code[:-1])
+
+codes = sys.stdin.read().split()
+print(sum(complexity(code, 2) for code in codes))
+print(sum(complexity(code, 25) for code in codes))

2024/input/21

@@ -0,0 +1,5 @@
+805A
+964A
+459A
+968A
+671A