Day 10.

10.py

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+import functools
+import itertools
+import operator
+
+
+def reverse_slice(input, start, length):
+    output = list(input)
+    for i, pos in enumerate(range(start, start + length)):
+        output[pos % len(output)] = input[(start + length - i - 1) % len(output)]
+    return output
+
+
+def do_rounds(lengths, count=1):
+    position, skip, data = 0, 0, list(range(256))
+    for _ in range(count):
+        for length in lengths:
+            data = reverse_slice(data, position, length)
+            position += length + skip
+            skip += 1
+    return data
+
+
+def group(n, iterable):
+    # https://docs.python.org/3.1/library/itertools.html#recipes
+    args = [iter(iterable)] * n
+    return itertools.zip_longest(*args)
+
+
+with open('data/10.txt', 'r') as file:
+    lengths = list(map(int, file.readline().strip().split(',')))
+    data = do_rounds(lengths)
+    print(f'Part one: {data[0]*data[1]}')
+
+
+with open('data/10.txt', 'r') as file:
+    lengths = list(map(ord, file.readline().strip())) + [17, 31, 73, 47, 23]
+    sparse_hash = do_rounds(lengths, 64)
+    dense_hash = [functools.reduce(operator.xor, g) for g in group(16, sparse_hash)]
+    # Yo dawg, I heard you like f-strings, so we put an f-string in your f-string.
+    print(f'Part two: {"".join(f"{c:02x}" for c in dense_hash)}')

data/10.txt

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+206,63,255,131,65,80,238,157,254,24,133,2,16,0,1,3