From 548b0bf9b212ab7d3dffe14bfc4b5b5e81c56152 Mon Sep 17 00:00:00 2001
From: hesham-ashraf <heshamashraf919@gmail.com>
Date: Sat, 7 Dec 2024 22:42:28 +0200
Subject: [PATCH] Radix Sort implementation

---
 Programs/Radix/RadixSort.java     | 80 +++++++++++++++++++++++++++++++
 Programs/Radix/RadixSortTest.java | 59 +++++++++++++++++++++++
 README.md                         |  2 +
 3 files changed, 141 insertions(+)
 create mode 100644 Programs/Radix/RadixSort.java
 create mode 100644 Programs/Radix/RadixSortTest.java

diff --git a/Programs/Radix/RadixSort.java b/Programs/Radix/RadixSort.java
new file mode 100644
index 0000000..7c885fa
--- /dev/null
+++ b/Programs/Radix/RadixSort.java
@@ -0,0 +1,80 @@
+// Radix sort Java implementation
+
+import java.io.*;
+import java.util.*;
+
+class Radix {
+
+    // A utility function to get maximum value in arr[]
+    static int getMax(int arr[], int n)
+    {
+        int mx = arr[0];
+        for (int i = 1; i < n; i++)
+            if (arr[i] > mx)
+                mx = arr[i];
+        return mx;
+    }
+
+    // A function to do counting sort of arr[] according to
+    // the digit represented by exp.
+    static void countSort(int arr[], int n, int exp)
+    {
+        int output[] = new int[n]; // output array
+        int i;
+        int count[] = new int[10];
+        Arrays.fill(count, 0);
+
+        // Store count of occurrences in count[]
+        for (i = 0; i < n; i++)
+            count[(arr[i] / exp) % 10]++;
+
+        // Change count[i] so that count[i] now contains
+        // actual position of this digit in output[]
+        for (i = 1; i < 10; i++)
+            count[i] += count[i - 1];
+
+        // Build the output array
+        for (i = n - 1; i >= 0; i--) {
+            output[count[(arr[i] / exp) % 10] - 1] = arr[i];
+            count[(arr[i] / exp) % 10]--;
+        }
+
+        // Copy the output array to arr[], so that arr[] now
+        // contains sorted numbers according to current
+        // digit
+        for (i = 0; i < n; i++)
+            arr[i] = output[i];
+    }
+
+    // The main function to that sorts arr[] of
+    // size n using Radix Sort
+    static void radixsort(int arr[], int n)
+    {
+        // Find the maximum number to know number of digits
+        int m = getMax(arr, n);
+
+        // Do counting sort for every digit. Note that
+        // instead of passing digit number, exp is passed.
+        // exp is 10^i where i is current digit number
+        for (int exp = 1; m / exp > 0; exp *= 10)
+            countSort(arr, n, exp);
+    }
+
+    // A utility function to print an array
+    static void print(int arr[], int n)
+    {
+        for (int i = 0; i < n; i++)
+            System.out.print(arr[i] + " ");
+    }
+
+    // Main driver method
+    public static void main(String[] args)
+    {
+        int arr[] = { 170, 45, 75, 90, 802, 24, 2, 66 };
+        int n = arr.length;
+
+        // Function Call
+        radixsort(arr, n);
+        print(arr, n);
+    }
+}
\ No newline at end of file
diff --git a/Programs/Radix/RadixSortTest.java b/Programs/Radix/RadixSortTest.java
new file mode 100644
index 0000000..db6ea59
--- /dev/null
+++ b/Programs/Radix/RadixSortTest.java
@@ -0,0 +1,59 @@
+import org.junit.jupiter.api.Test;
+import static org.junit.jupiter.api.Assertions.assertArrayEquals;
+
+class RadixSortTest {
+
+    @Test
+    void testRadixSortWithPositiveNumbers() {
+        int[] input = {170, 45, 75, 90, 802, 24, 2, 66};
+        int[] expected = {2, 24, 45, 66, 75, 90, 170, 802};
+
+        Radix.radixsort(input, input.length);
+        assertArrayEquals(expected, input, "The sorted array does not match the expected output");
+    }
+
+    @Test
+    void testRadixSortWithAllEqualNumbers() {
+        int[] input = {5, 5, 5, 5, 5};
+        int[] expected = {5, 5, 5, 5, 5};
+
+        Radix.radixsort(input, input.length);
+        assertArrayEquals(expected, input, "The sorted array does not match the expected output");
+    }
+
+    @Test
+    void testRadixSortWithSingleElement() {
+        int[] input = {42};
+        int[] expected = {42};
+
+        Radix.radixsort(input, input.length);
+        assertArrayEquals(expected, input, "The sorted array does not match the expected output");
+    }
+
+    @Test
+    void testRadixSortWithAlreadySortedArray() {
+        int[] input = {1, 2, 3, 4, 5};
+        int[] expected = {1, 2, 3, 4, 5};
+
+        Radix.radixsort(input, input.length);
+        assertArrayEquals(expected, input, "The sorted array does not match the expected output");
+    }
+
+    @Test
+    void testRadixSortWithDescendingArray() {
+        int[] input = {9, 8, 7, 6, 5, 4, 3, 2, 1};
+        int[] expected = {1, 2, 3, 4, 5, 6, 7, 8, 9};
+
+        Radix.radixsort(input, input.length);
+        assertArrayEquals(expected, input, "The sorted array does not match the expected output");
+    }
+
+    @Test
+    void testRadixSortWithEmptyArray() {
+        int[] input = {};
+        int[] expected = {};
+
+        Radix.radixsort(input, input.length);
+        assertArrayEquals(expected, input, "The sorted array does not match the expected output");
+    }
+}
diff --git a/README.md b/README.md
index cb3d676..8a34e11 100644
--- a/README.md
+++ b/README.md
@@ -126,6 +126,8 @@ It is very easy to contribute, you may follow these steps -
 99.[RotateLinkedList](https://github.com/PrajaktaSathe/Java/blob/main/Programs/RotateLinkedList.java)-Program to demo rotating a linked list
 100. [ReverseString](https://github.com/PrajaktaSathe/Java/blob/main/ReverseString.java) -Program to reverse a String using the java method substring.
 101.[Overriding](https://github.com/PrajaktaSathe/Java/blob/main/Programs/Overriding.java)-Program to demo overriding in java
+102. [Radix Sort](https://github.com/PrajaktaSathe/Java/blob/main/Programs/Radix/RadixSort.java)-Program to demo Radix Sort in java
+
 
 # Contributors - 
 ## A big thank you to all our contributors!!!