Day 16: Add Python solution

16/input.txt

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16/solution.py

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+#!/usr/bin/env python3
+
+import sys
+from operator import mul
+from functools import reduce
+from itertools import tee, takewhile, islice
+
+packet = sys.stdin.readline().rstrip()
+bitstr = "".join([f"{int(x,16):04b}" for x in packet])
+
+ops = {
+    0: sum,
+    1: lambda l: reduce(mul, l, 1),
+    2: min,
+    3: max,
+    5: lambda l: 1 if l[0] > l[1] else 0,
+    6: lambda l: 1 if l[0] < l[1] else 0,
+    7: lambda l: 1 if l[0] == l[1] else 0,
+}
+
+def decode(p):
+    ver = int(p[0:3],2)
+    pid = int(p[3:6],2)
+    versum = ver
+
+    if pid == 4:
+        a, b = tee(map(lambda b: (int(b[0],2), int("".join(b[1:]), 2)),
+                       zip(*(iter(p[6:]),)*5)))
+        n = sum(takewhile(lambda s: s, map(lambda x: x[0], a))) + 1
+        val = reduce(lambda a, b: a << 4 | b[1], islice(b, n), 0)
+        plen = 6 + n * 5
+
+        return plen, val, ver
+    else:
+        typ = int(p[6],2)
+        rvals = []
+        start = 7+(11 if typ else 15)
+        plen = int(p[7:start],2)
+        if typ:
+            for i in range(plen):
+                l, v, vn = decode(p[start:])
+                rvals.append(v)
+                start += l
+                versum+=vn
+        else:
+            while plen:
+                l, v, vn = decode(p[start:start+plen])
+                rvals.append(v)
+                start += l
+                plen -= l
+                versum+=vn
+
+        rval = ops[pid](rvals)
+        return start, rval, versum
+
+_, gold, silver = decode(bitstr)
+print(f"Silver: {silver}\nGold: {gold}")