Solve 2016 day 16.

2016/d16.py

@@ -0,0 +1,42 @@
+def step(a: str) -> str:
+    b = "".join(["1" if c == "0" else "0" for c in reversed(a)])
+    return a + "0" + b
+
+
+def fill(a: str, n: int) -> str:
+    while len(a) < n:
+        a = step(a)
+    return a[:n]
+
+
+def checksum(a: str) -> str:
+    while len(a) % 2 == 0:
+        xs = []
+        for i in range(0, len(a), 2):
+            if a[i] == a[i + 1]:
+                xs.append("1")
+            else:
+                xs.append("0")
+        a = "".join(xs)
+    return a
+
+
+def solve():
+    assert step("1") == "100"
+    assert step("0") == "001"
+    assert step("11111") == "11111000000"
+
+    with open("i16.txt") as f:
+        d = f.read().strip()
+
+    a = fill(d, 272)
+    b = checksum(a)
+    print(b)
+
+    a = fill(d, 35651584)
+    b = checksum(a)
+    print(b)
+
+
+if __name__ == "__main__":
+    solve()