From 2cfe146e9d27878f2e770044b3b79ee845c0e787 Mon Sep 17 00:00:00 2001
From: Dmitry Kokorin <dmitry@kokorin.org>
Date: Wed, 23 Mar 2016 14:46:33 +0300
Subject: [PATCH] difference_of_squares: iteration 1

---
 .../difference_of_squares.h                   | 34 +++++++++++++++++++
 1 file changed, 34 insertions(+)
 create mode 100644 cpp/difference-of-squares/difference_of_squares.h

diff --git a/cpp/difference-of-squares/difference_of_squares.h b/cpp/difference-of-squares/difference_of_squares.h
new file mode 100644
index 0000000..25c69e4
--- /dev/null
+++ b/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);
+}
+
+}