chore: import upstream snapshot with attribution

sorting/radix_sort.cpp

@@ -0,0 +1,58 @@
+#include <cmath>
+#include <cstdlib>
+#include <cstring>
+#include <iostream>
+
+void radixsort(int a[], int n) {
+    int count[10];
+    int* output = new int[n];
+    memset(output, 0, n * sizeof(*output));
+    memset(count, 0, sizeof(count));
+    int max = 0;
+    for (int i = 0; i < n; ++i) {
+        if (a[i] > max) {
+            max = a[i];
+        }
+    }
+    int maxdigits = 0;
+    while (max) {
+        maxdigits++;
+        max /= 10;
+    }
+    for (int j = 0; j < maxdigits; j++) {
+        for (int i = 0; i < n; i++) {
+            int t = std::pow(10, j);
+            count[(a[i] % (10 * t)) / t]++;
+        }
+        int k = 0;
+        for (int p = 0; p < 10; p++) {
+            for (int i = 0; i < n; i++) {
+                int t = std::pow(10, j);
+                if ((a[i] % (10 * t)) / t == p) {
+                    output[k] = a[i];
+                    k++;
+                }
+            }
+        }
+        memset(count, 0, sizeof(count));
+        for (int i = 0; i < n; ++i) {
+            a[i] = output[i];
+        }
+    }
+    delete[] output;
+}
+
+void print(int a[], int n) {
+    for (int i = 0; i < n; ++i) {
+        std::cout << a[i] << " ";
+    }
+    std::cout << std::endl;
+}
+
+int main() {
+    int a[] = {170, 45, 75, 90, 802, 24, 2, 66};
+    int n = sizeof(a) / sizeof(a[0]);
+    radixsort(a, n);
+    print(a, n);
+    return 0;
+}