huge commit

2026/cscg/rev/go-backup/decode.py

@@ -0,0 +1,71 @@
+EANS = [
+    "4932413071222",
+    "9215337181228",
+    "4055572232713",
+    "3177777536937",
+    "5194353145886",
+    "8022631001531",
+    "2177559451930",
+    "9375914288310",
+]
+
+ISBNS = [
+    "0-024-00310-7",
+    "0-238-30610-0",
+    "3-505-52102-7",
+    "0-022-11111-5",
+    "6-052-75101-0",
+    "8-323-17020-7",
+    "6-422-29100-0",
+    "5-112-73112-5",
+]
+
+cards = [
+    "5217804766545209",
+    "4885373827486781",
+    "5839899598496843",
+    "9587981988999895",
+    "8837998849894933",
+    "8986989999966281",
+    "9999992947693935",
+    "9999489398999945",
+]
+
+
+def decode_ean(ean):
+    digits = [int(c) for c in ean[:12]]
+    total = 0
+    for i, d in enumerate(digits):
+        if i % 2 != 0:
+            total += d * 3
+        else:
+            total += d
+    return chr(total)
+
+
+def decode_isbn(isbn):
+    digits = [int(c) for c in isbn.replace("-", "")[:9]]
+    total = sum((i + 1) * d for i, d in enumerate(digits))
+    return chr(total)
+
+
+def decode_credit_card(cc):
+    digits = [int(c) for c in cc[:15]]
+    total = 0
+    for idx in range(14, -1, -1):
+        d = digits[14 - idx]
+        weight = 14 - idx
+        if weight % 2 != 0:
+            total += d
+        else:
+            doubled = 2 * d
+            total += doubled - 9 if doubled > 9 else doubled
+    return chr(total)
+
+
+part1 = "".join(decode_ean(i) for i in EANS)
+part2 = "".join(decode_isbn(i) for i in ISBNS)
+part3 = "".join(decode_credit_card(c) for c in cards)
+
+
+print(part1 + part2 + part3)