Add Radix Sort implementation in radix_sort.ts

Implement Radix Sort algorithm with Counting Sort as a helper function.

Author: saviour2

sorts/radix_sort.ts

@@ -0,0 +1,67 @@
+/**
+ * Radix Sort is a non-comparison integer sorting algorithm that sorts integers
+ * by processing individual digits. It sorts by grouping keys by the individual
+ * digits which share the same significant position and value.
+ *
+ * Time Complexity: O(d * (n + b)) where d is the number of digits in the
+ * largest number, n is the size of the input, and b is the base (10 for decimal).
+ *
+ * For more info: https://en.wikipedia.org/wiki/Radix_sort
+ */
+
+// A helper function for Radix Sort that uses Counting Sort to sort the elements
+// based on a significant digit.
+function countingSortForRadix(array: number[], digit: number): number[] {
+  const n = array.length;
+  const output: number[] = new Array(n).fill(0);
+  const count: number[] = new Array(10).fill(0);
+
+  // Store count of occurrences in count[]
+  for (let i = 0; i < n; i++) {
+    const index = Math.floor(array[i] / digit) % 10;
+    count[index]++;
+  }
+
+  // Change count[i] so that count[i] now contains the actual
+  // position of this digit in output[]
+  for (let i = 1; i < 10; i++) {
+    count[i] += count[i - 1];
+  }
+
+  // Build the output array. We iterate from the end to make it a stable sort.
+  for (let i = n - 1; i >= 0; i--) {
+    const index = Math.floor(array[i] / digit) % 10;
+    output[count[index] - 1] = array[i];
+    count[index]--;
+  }
+
+  return output;
+}
+
+export function radixSort(array: number[]): number[] {
+  if (array.length === 0) {
+    return [];
+  }
+
+  // Create a copy to avoid modifying the original array (pure function)
+  let result = [...array];
+
+  // Find the maximum number to know the number of digits
+  const maxNumber = Math.max(...result);
+
+  // Do counting sort for every digit. Note that instead of passing digit
+  // number, digit is passed. digit is 10^i where i is current digit number.
+  for (let digit = 1; Math.floor(maxNumber / digit) > 0; digit *= 10) {
+    result = countingSortForRadix(result, digit);
+  }
+
+  return result;
+}
+
+// --- Example Usage ---
+if (require.main === module) {
+  const unsortedArray = [170, 45, 75, 90, 802, 24, 2, 66];
+  console.log('Original Array:', unsortedArray);
+  const sortedArray = radixSort(unsortedArray);
+  console.log('Sorted Array:', sortedArray); // Output: [ 2, 24, 45, 66, 75, 90, 170, 802 ]
+}