From 228dbff64344353848797adce97534e3d450a572 Mon Sep 17 00:00:00 2001
From: Gourav Suri <gourav.suri@grabtaxi.com>
Date: Sat, 23 Oct 2021 02:10:54 +0530
Subject: [PATCH] added radix sort to the deck of sorting algorithms

---
 README.md                   |  1 +
 RadixSort/RadixSort.go      | 38 +++++++++++++++++++++++++++++++++++++
 RadixSort/RadixSort_test.go | 19 +++++++++++++++++++
 3 files changed, 58 insertions(+)
 create mode 100644 RadixSort/RadixSort.go
 create mode 100644 RadixSort/RadixSort_test.go

diff --git a/README.md b/README.md
index 90c81b4..213823a 100644
--- a/README.md
+++ b/README.md
@@ -39,6 +39,7 @@ There are several data structures and algorithms implemented in this project. Th
 - Cocktail Sort
 - Gnome Sort
 - Merge Sort
+- Radix Sort
 
 ## Usage
 
diff --git a/RadixSort/RadixSort.go b/RadixSort/RadixSort.go
new file mode 100644
index 0000000..657b657
--- /dev/null
+++ b/RadixSort/RadixSort.go
@@ -0,0 +1,38 @@
+package RadixSort
+
+import (
+	"bytes"
+	"encoding/binary"
+)
+
+const digit = 4
+const maxbit = -1 << 31
+
+func RadixSort(data []int) {
+	buf := bytes.NewBuffer(nil)
+	ds := make([][]byte, len(data))
+	for i, e := range data {
+		binary.Write(buf, binary.LittleEndian, e^maxbit)
+		b := make([]byte, digit)
+		buf.Read(b)
+		ds[i] = b
+	}
+	countingSort := make([][][]byte, 256)
+	for i := 0; i < digit; i++ {
+		for _, b := range ds {
+			countingSort[b[i]] = append(countingSort[b[i]], b)
+		}
+		j := 0
+		for k, bs := range countingSort {
+			copy(ds[j:], bs)
+			j += len(bs)
+			countingSort[k] = bs[:0]
+		}
+	}
+	var w int32
+	for i, b := range ds {
+		buf.Write(b)
+		binary.Read(buf, binary.LittleEndian, &w)
+		data[i] = int(w^maxbit)
+	}
+}
diff --git a/RadixSort/RadixSort_test.go b/RadixSort/RadixSort_test.go
new file mode 100644
index 0000000..c12188a
--- /dev/null
+++ b/RadixSort/RadixSort_test.go
@@ -0,0 +1,19 @@
+package RadixSort
+
+import (
+	"sort"
+	"testing"
+)
+
+func TestRadixSort(t *testing.T) {
+	array1 := []int{421, 15, -175, 90, -2, 214, -52, -166}
+	array2 := make(sort.IntSlice, len(array1))
+	copy(array2, array1)
+	RadixSort(array1)
+	array2.Sort()
+	for i := range array1 {
+		if array1[i] != array2[i] {
+			t.Fail()
+		}
+	}
+}