1 files changed, 47 insertions, 42 deletions
diff --git a/gcd.cpp b/gcd.cpp
index 659c77a..e1d363a 100644
--- a/gcd.cpp
+++ b/gcd.cpp
@@ -7,65 +7,70 @@
  *
  *
  * To use GNU Multiple Precision Arithmetic Library:
- * 
- * # g++ -o gcd-cpp-gmp -DGMP -lgmpxx -lgmp gcd.cpp
+ *
+ * # g++ -DGMP gcd.cpp -lgmpxx -lgmp -o gcd-cpp-gmp
  * # ./gcd-cpp-gmp 1234567890987654321 987654321234567
  * # 63
  *
  */
 
-
 #include <cstdlib>
 #include <iostream>
-#include <vector>
 #include <sstream>
-
-using namespace std;
+#include <vector>
+#if __cplusplus >= 201703L
+#include <execution>
+#include <numeric>
+#endif
 
 #ifdef GMP
-    #include <gmpxx.h>
-    typedef mpz_class Number;
+#include <gmpxx.h>
+typedef mpz_class Number;
 #else
-    typedef unsigned int Number;
-#endif // GMP
+typedef unsigned long Number;
+#endif
 
-typedef vector<Number> Numbers;
+using std::vector;
 
-Number gcd(Number a, Number b)
-{
-    Number c;
-    while (b != 0) {
-        c = b;
-        b = a % b;
-        a = c;
-    }
-    return a;
+template <class N> N gcd2(N a, N b) {
+  while (b != 0) {
+    N c = b;
+    b = a % b;
+    a = c;
+  }
+  return a;
 }
 
-Number gcd(const Numbers & ns)
-{
-    Number r = 0;
-    for(Numbers::const_iterator n = ns.begin(); n != ns.end(); ++n)
-        r = gcd(*n, r);
-    return r;
+#if __cplusplus >= 201703L
+template <class N> class GCD {
+public:
+  N operator()(N a, N b) const { return gcd2(a, b); };
+};
+
+template <class N> N gcd(const vector<N> &ns) {
+  GCD<N> GCD;
+  return reduce(std::execution::par, begin(ns), end(ns), N(0), GCD);
 }
 
+#else
 
-int main (int argc, char *argv[])
-{
-    if (argc > 1) {
-        Numbers ns(argc - 1);
-        for(int n = 1; n < argc; ++n) {
-            stringstream str;
-            str << argv[n];
-            str >> ns[n-1];
-            /* NOTE:
-             * For GMP we can just assign: ns[n-1] = argv[n],
-             * and sstream is not needed.
-             */
-        }
-        cout << gcd(ns) << endl;
-    }
-    return EXIT_SUCCESS;
+template <class N> N gcd(const vector<N> &ns) {
+  N r = 0;
+  for (typename vector<N>::const_iterator n = ns.begin(); n != ns.end(); ++n)
+    r = gcd2(*n, r);
+  return r;
 }
+#endif
 
+int main(int argc, char *argv[]) {
+  if (argc > 1) {
+    vector<Number> ns(argc - 1);
+    for (int n = 1; n < argc; ++n) {
+      std::stringstream str;
+      str << argv[n];
+      str >> ns[n - 1];
+    }
+    std::cout << gcd(ns) << std::endl;
+  }
+  return EXIT_SUCCESS;
+}