difference_of_squares: iteration 1

cpp/difference-of-squares/difference_of_squares.h

@@ -0,0 +1,34 @@
+#pragma once
+
+#define EXERCISM_RUN_ALL_TESTS
+
+
+namespace squares {
+
+namespace detail {
+
+constexpr unsigned sum(unsigned n)
+{
+    return (n*(n+1))/2;
+}
+
+}
+
+
+constexpr unsigned square_of_sums(unsigned n)
+{
+    using detail::sum;
+    return sum(n)*sum(n);
+}
+
+constexpr unsigned sum_of_squares(unsigned n)
+{
+    return (n*(n+1)*(2*n+1))/6;
+}
+
+constexpr unsigned difference(unsigned n)
+{
+    return square_of_sums(n) - sum_of_squares(n);
+}
+
+}