Create Radix_sort.java

Sorting_Algorithms_JAVA/Radix_sort.java

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+import java.util.Arrays;
+
+public class RadixSort {
+
+    /**
+     * The main function that sorts arr[] using Radix Sort.
+     */
+    public void sort(int[] arr) {
+        if (arr == null || arr.length == 0) {
+            return;
+        }
+
+        // 1. Find the maximum number to know the number of digits.
+        int max = getMax(arr);
+
+        // 2. Do counting sort for every digit.
+        // We use 'exp' (exponent) to represent the current digit's place
+        // (1, 10, 100, 1000...)
+        for (int exp = 1; max / exp > 0; exp *= 10) {
+            countingSortByDigit(arr, exp);
+        }
+    }
+
+    /**
+     * A utility function to get the maximum value in arr[].
+     */
+    private int getMax(int[] arr) {
+        int max = arr[0];
+        for (int i = 1; i < arr.length; i++) {
+            if (arr[i] > max) {
+                max = arr[i];
+            }
+        }
+        return max;
+    }
+
+    /**
+     * A stable sort (Counting Sort) to sort array elements
+     * based on the digit at the 'exp' place.
+     */
+    private void countingSortByDigit(int[] arr, int exp) {
+        int n = arr.length;
+        int[] output = new int[n]; // The sorted output array
+        int[] count = new int[10]; // To store count of digits (0-9)
+
+        // Initialize count array to all zeros
+        Arrays.fill(count, 0);
+
+        // 1. Store count of occurrences of each digit
+        for (int i = 0; i < n; i++) {
+            // Get the digit at the 'exp' place
+            int digit = (arr[i] / exp) % 10;
+            count[digit]++;
+        }
+
+        // 2. Change count[i] so that it now contains the
+        //    actual position of this digit in output[]
+        for (int i = 1; i < 10; i++) {
+            count[i] += count[i - 1];
+        }
+
+        // 3. Build the output array
+        // We go in reverse order to make the sort stable
+        for (int i = n - 1; i >= 0; i--) {
+            int digit = (arr[i] / exp) % 10;
+
+            // Place the element at its correct sorted position
+            output[count[digit] - 1] = arr[i];
+
+            // Decrement the count for that digit
+            count[digit]--;
+        }
+
+        // 4. Copy the sorted output array back to arr[]
+        System.arraycopy(output, 0, arr, 0, n);
+    }
+
+    /**
+     * A main method to test the sort.
+     */
+    public static void main(String[] args) {
+        int[] data = {170, 45, 75, 90, 802, 24, 2, 66};
+
+        System.out.println("Original array: " + Arrays.toString(data));
+
+        RadixSort sorter = new RadixSort();
+        sorter.sort(data);
+
+        System.out.println("Sorted array:   " + Arrays.toString(data));
+    }
+}