feat: Add Radix sort. (#8)

Author: goloroden

README.md

@@ -9,6 +9,7 @@ So far, the following exercises have been covered:
 - [Autocomplete](./autocomplete/) – implements an autocomplete feature using a trie
 - [Continous maximum](./continuousmax/) – calculates the maximum of a sliding window
 - [Heap](./heap/) – implements a heap from scratch, without using the built-in `container/heap` package
+- [Radix sort](./radixsort/) – implements radix sort
 - [Remove k-th last element](./removekthlastelement/) – removes the k-th last element from a single-linked list
 - [Running median](./runningmedian/) – calculates the running median of a sequence of numbers
 - [Tic tac toe](./tictactoe/) – detects winnning states in a tic tac toe game

radixsort/documentation.go

@@ -0,0 +1,2 @@
+// Package radixsort implements radix sort.
+package radixsort

radixsort/radix_sort.go

@@ -0,0 +1,46 @@
+package radixsort
+
+import (
+	"math"
+)
+
+func max(values []int) int {
+	maxValue := math.MinInt
+	for _, value := range values {
+		if value > maxValue {
+			maxValue = value
+		}
+	}
+	return maxValue
+}
+
+func countDigits(number int) int {
+	if number == 0 {
+		return 1
+	}
+	return int(math.Log10(float64(number))) + 1
+}
+
+func getDigit(number, n int) int {
+	return (number / int(math.Pow(10, float64(n)))) % 10
+}
+
+func Sort(values []int) []int {
+	digits := countDigits(max(values))
+
+	for k := 0; k < digits; k++ {
+		buckets := make([][]int, 10)
+
+		for _, value := range values {
+			digit := getDigit(value, k)
+			buckets[digit] = append(buckets[digit], value)
+		}
+
+		values = []int{}
+		for _, bucket := range buckets {
+			values = append(values, bucket...)
+		}
+	}
+
+	return values
+}

radixsort/radix_sort_test.go

@@ -0,0 +1,15 @@
+package radixsort_test
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/thenativeweb/codingcircle/radixsort"
+)
+
+func TestSort(t *testing.T) {
+	unsorted := []int{12, 27, 2, 17, 9, 8}
+	sorted := []int{2, 8, 9, 12, 17, 27}
+
+	assert.Equal(t, sorted, radixsort.Sort(unsorted))
+}