Kata 05

kata-05-bloom-filters/bloom_filters.py

@@ -0,0 +1,115 @@
+# test_array = [0, 0, 0]
+#
+# users = {
+#     1: "slavi",
+#     2: "nasko",
+#     3: "stoqn"
+# }
+#
+# user_hashes = []
+#
+# for user in users.values():
+#     user_hash = str(hash(user))
+#
+#     print(f"Hash for {user} is {user_hash}")
+#     user_hashes.append(user_hash)
+#
+# print("user_hashes", user_hashes)
+
+
+# import hashlib
+#
+# class BloomFilter:
+#     def __init__(self, size=1000, hash_count=3):
+#         self.size = size
+#         self.hash_count = hash_count
+#         self.bit_array = [0] * size
+#
+#     def _hashes(self, item):
+#         digest = hashlib.md5(item.encode()).hexdigest()
+#
+#         for i in range(self.hash_count):
+#             chunk = digest[i*8:(i+1)*8]
+#             yield int(chunk, 16) % self.size
+#
+#     def add(self, item):
+#         for index in self._hashes(item):
+#             self.bit_array[index] = 1
+#
+#     def contains(self, item):
+#         for index in self._hashes(item):
+#             if self.bit_array[index] == 0:
+#                 return False
+#         return True
+#
+# users = ["slavi", "nasko", "stoqn"]
+#
+# bf = BloomFilter(size=100, hash_count=3)
+#
+# for user in users:
+#     bf.add(user)
+#
+# print("bf", bf)
+#
+# print(bf.contains("slavi"))   # True
+# print(bf.contains("nasko"))   # True
+# print(bf.contains("pesho"))   # False (or sometimes True → false positive)
+
+# The Simplest Membership Filter
+# X - slow, memory-heavy
+class WordSet:
+    def __init__(self):
+        self.words = []
+
+    def add(self, word):
+        self.words.append(word)
+
+    def contains(self, word):
+        return word in self.words
+
+
+class MarkerArray:
+    def __init__(self, size):
+        self.size = size
+        self.slots = [0] * size # Represented like [0, 0, 0, 0, 0, 0]
+
+
+class MultiHasher:
+    def __init__(self, size, count):
+        self.size = size
+        self.count = count
+
+    def hashes(self, word):
+        for i in range(self.count):
+            total = 0
+            for char in word:
+                total += ord(char) * (i + 1)
+            yield total % self.size
+
+
+class BloomFilter:
+    def __init__(self, size=20, hash_count=3):
+        self.array = MarkerArray(size)
+        self.hasher = MultiHasher(size, hash_count)
+
+    def add(self, word):
+        for index in self.hasher.hashes(word):
+            self.array.slots[index] = 1
+
+    def contains(self, word):
+        for index in self.hasher.hashes(word):
+            if self.array.slots[index] == 0:
+                return False
+        return True
+
+
+bf = BloomFilter(10)
+
+bf.add("cat")
+bf.add("dog")
+
+print(bf.contains("cat"))   # True
+print(bf.contains("dog"))   # True
+print(bf.contains("god"))   # ❗ Maybe True
+
+# TODO: Truly understand what is going on and exercise bit operations