From 4e515e9bd530b3b6d5725bf8cb2024124e4171d1 Mon Sep 17 00:00:00 2001
From: Marcel Edmund Franke <marcel.edmund.franke@gmail.com>
Date: Sat, 2 Mar 2024 15:35:19 +0100
Subject: [PATCH] Strutil: HammingDistance func

The Hamming distance is the number of positions at which the corresponding symbols are different
---
 strutil/string.go              | 22 ++++++++++++++++++++++
 strutil/string_example_test.go | 13 +++++++++++++
 strutil/string_test.go         | 23 +++++++++++++++++++++++
 3 files changed, 58 insertions(+)

diff --git a/strutil/string.go b/strutil/string.go
index b8785fa..9aa423f 100644
--- a/strutil/string.go
+++ b/strutil/string.go
@@ -4,6 +4,7 @@
 package strutil
 
 import (
+	"errors"
 	"regexp"
 	"strings"
 	"unicode"
@@ -594,3 +595,24 @@ func SubInBetween(str string, start string, end string) string {
 
 	return ""
 }
+
+// HammingDistance calculates the Hamming distance between two strings.
+// The Hamming distance is the number of positions at which the corresponding symbols are different.
+// This func returns an error if the input strings are of unequal lengths.
+func HammingDistance(a, b string) (int, error) {
+	if len(a) != len(b) {
+		return -1, errors.New("a length and b length are unequal")
+	}
+
+	ar := []rune(a)
+	br := []rune(b)
+
+	var distance int
+	for i, codepoint := range ar {
+		if codepoint != br[i] {
+			distance++
+		}
+	}
+
+	return distance, nil
+}
diff --git a/strutil/string_example_test.go b/strutil/string_example_test.go
index 54adfda..a9bcb28 100644
--- a/strutil/string_example_test.go
+++ b/strutil/string_example_test.go
@@ -667,3 +667,16 @@ func ExampleSubInBetween() {
 	// abc
 	// bc
 }
+
+func ExampleHammingDistance() {
+
+	result, _ := HammingDistance("abc", "def")
+	fmt.Println(result)
+
+	result, _ = HammingDistance("name", "namf")
+	fmt.Println(result)
+
+	// Output:
+	// 3
+	// 1
+}
diff --git a/strutil/string_test.go b/strutil/string_test.go
index 10c6135..3d94af0 100644
--- a/strutil/string_test.go
+++ b/strutil/string_test.go
@@ -581,3 +581,26 @@ func TestSubInBetween(t *testing.T) {
 	assert.Equal("", SubInBetween(str, "a", ""))
 	assert.Equal("", SubInBetween(str, "a", "f"))
 }
+
+func TestHammingDistance(t *testing.T) {
+	assert := internal.NewAssert(t, "HammingDistance")
+
+	hd := func(a, b string) int {
+		c, _ := HammingDistance(a, b)
+		return c
+	}
+
+	assert.Equal(0, hd(" ", " "))
+	assert.Equal(1, hd(" ", "c"))
+	assert.Equal(1, hd("a", "d"))
+	assert.Equal(1, hd("a", " "))
+	assert.Equal(1, hd("a", "f"))
+
+	assert.Equal(0, hd("", ""))
+	assert.Equal(-1, hd("abc", "ab"))
+	assert.Equal(3, hd("abc", "def"))
+	assert.Equal(-1, hd("kitten", "sitting"))
+	assert.Equal(1, hd("ö", "ü"))
+	assert.Equal(0, hd("日本語", "日本語"))
+	assert.Equal(3, hd("日本語", "語日本"))
+}