From 8d671ff778c55af06e38806a3f96602b3301ad4f Mon Sep 17 00:00:00 2001
From: dece <shgck@pistache.land>
Date: Fri, 17 Dec 2021 17:28:07 +0100
Subject: [PATCH] Day 16

---
 2021/day16.py | 61 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 61 insertions(+)
 create mode 100644 2021/day16.py

diff --git a/2021/day16.py b/2021/day16.py
new file mode 100644
index 0000000..8107818
--- /dev/null
+++ b/2021/day16.py
@@ -0,0 +1,61 @@
+from functools import reduce
+from operator import mul
+
+with open("input16.txt") as f:
+    line = f.read().rstrip()
+fdata = ""
+for i in range(len(line) // 2):
+    fdata += f"{int(line[i*2:i*2+2], 16):08b}"
+version_sum = 0
+
+
+def parse_packets(data, maxp=None):
+    global version_sum
+    c = 0
+    p = 0
+    values = []
+    while (maxp is None or p < maxp) and c < len(data) - 8:
+        version = int(data[c:c+3], 2)
+        version_sum += version
+        tid = int(data[c+3:c+6], 2)
+        c += 6
+        if tid == 4:
+            bits = ""
+            while True:
+                stop_reading = data[c] == "0"
+                bits += data[c+1:c+5]
+                c += 5
+                if stop_reading:
+                    break
+            values.append(int(bits, 2))
+        else:
+            if data[c] == "0":
+                num_bits = int(data[c+1:c+16], 2)
+                c += 16
+                nc, nv = parse_packets(data[c:c+num_bits])
+            else:
+                num_subs = int(data[c+1:c+12], 2)
+                c += 12
+                nc, nv = parse_packets(data[c:], maxp=num_subs)
+            c += nc
+            if tid == 0:
+                values.append(sum(nv))
+            elif tid == 1:
+                values.append(reduce(mul, nv, 1))
+            elif tid == 2:
+                values.append(min(nv))
+            elif tid == 3:
+                values.append(max(nv))
+            elif tid == 5:
+                values.append(1 if nv[0] > nv[1] else 0)
+            elif tid == 6:
+                values.append(1 if nv[0] < nv[1] else 0)
+            elif tid == 7:
+                values.append(1 if nv[0] == nv[1] else 0)
+        p += 1
+    return c, values
+
+
+_, values = parse_packets(fdata)
+print(version_sum)
+print(values[0])