feat: Add new example.

Author: goloroden

README.md

@@ -7,6 +7,7 @@ codingcircle contains the examples from the YouTube Coding Cirle.
 So far, the following exercises have been covered:
 
 - [Autocomplete](./autocomplete/) – implements an autocomplete feature using a trie
+- [Bloom filter](./bloomfilter/) – implements a bloom filter
 - [Busfactor](./busfactor/) – calculates the the maximum load of a bus based on events
 - [Clever max](./clevermax/) – calculates the maximum of two numbers
 - [Cons, Car, Cdr & co.](./cons) – implements a cons cell and the corresponding functions

bloomfilter/bloomfilter.go

@@ -0,0 +1,56 @@
+package bloomfilter
+
+import (
+	"crypto/sha1"
+	"strconv"
+)
+
+type BloomFilter struct {
+	bitArray  []bool
+	size      int
+	numHashes int
+}
+
+func NewBloomFilter(size, numHashes int) *BloomFilter {
+	return &BloomFilter{
+		bitArray:  make([]bool, size),
+		size:      size,
+		numHashes: numHashes,
+	}
+}
+
+func (bf *BloomFilter) Add(value string) {
+	for i := 0; i < bf.numHashes; i++ {
+		hash := sha1.New()
+		hash.Write([]byte(value + strconv.Itoa(i)))
+		digest := hash.Sum(nil)
+
+		index := int(digest[0])<<24 | int(digest[1])<<16 | int(digest[2])<<8 | int(digest[3])
+		index = index % bf.size
+		if index < 0 {
+			index += bf.size
+		}
+
+		bf.bitArray[index] = true
+	}
+}
+
+func (bf *BloomFilter) Contains(value string) bool {
+	for i := 0; i < bf.numHashes; i++ {
+		hash := sha1.New()
+		hash.Write([]byte(value + strconv.Itoa(i)))
+		digest := hash.Sum(nil)
+
+		index := int(digest[0])<<24 | int(digest[1])<<16 | int(digest[2])<<8 | int(digest[3])
+		index = index % bf.size
+		if index < 0 {
+			index += bf.size
+		}
+
+		if !bf.bitArray[index] {
+			return false
+		}
+	}
+
+	return true
+}

bloomfilter/bloomfilter_test.go

@@ -0,0 +1,19 @@
+package bloomfilter_test
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/thenativeweb/codingcircle/bloomfilter"
+)
+
+func TestBloomFilter(t *testing.T) {
+	bf := bloomfilter.NewBloomFilter(512, 5)
+
+	bf.Add("www.example.com")
+	bf.Add("dangerous.example.com")
+
+	assert.True(t, bf.Contains("www.example.com"))
+	assert.True(t, bf.Contains("dangerous.example.com"))
+	assert.False(t, bf.Contains("www.thenativeweb.io"))
+}

bloomfilter/documentation.go

@@ -0,0 +1,2 @@
+// Package bloomfilter implements a bloom filter.
+package bloomfilter