Add code for 2015 advent that I did historically.

day_4/solution.py

@@ -0,0 +1,19 @@
+import hashlib
+
+passkey = input("Input passkey here: ")
+
+
+def find_suffix(passkey, leading_zeroes):
+	hexkey = ""
+	suffix = 0
+
+	while hexkey[:leading_zeroes] != "0" * leading_zeroes:
+		suffix += 1
+		hashkey = hashlib.md5(f"{passkey}{suffix}".encode())
+		hexkey = hashkey.hexdigest()
+
+	return suffix
+
+
+print(f"Part 1 Suffix = {find_suffix(passkey, 5)}")
+print(f"Part 2 Suffix = {find_suffix(passkey, 6)}")