Data commit

Task/Pancake-numbers/Python/pancake-numbers.py

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+"""Pancake numbers. Requires Python>=3.7."""
+import time
+
+from collections import deque
+from operator import itemgetter
+from typing import Tuple
+
+Pancakes = Tuple[int, ...]
+
+
+def flip(pancakes: Pancakes, position: int) -> Pancakes:
+    """Flip the stack of pancakes at the given position."""
+    return tuple([*reversed(pancakes[:position]), *pancakes[position:]])
+
+
+def pancake(n: int) -> Tuple[Pancakes, int]:
+    """Return the nth pancake number."""
+    init_stack = tuple(range(1, n + 1))
+    stack_flips = {init_stack: 0}
+    queue = deque([init_stack])
+
+    while queue:
+        stack = queue.popleft()
+        flips = stack_flips[stack] + 1
+
+        for i in range(2, n + 1):
+            flipped = flip(stack, i)
+            if flipped not in stack_flips:
+                stack_flips[flipped] = flips
+                queue.append(flipped)
+
+    return max(stack_flips.items(), key=itemgetter(1))
+
+
+if __name__ == "__main__":
+    start = time.time()
+
+    for n in range(1, 10):
+        pancakes, p = pancake(n)
+        print(f"pancake({n}) = {p:>2}. Example: {list(pancakes)}")
+
+    print(f"\nTook {time.time() - start:.3} seconds.")