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Telegram/ThirdParty/range-v3/example/comprehensions.cpp

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+// Range v3 library
+//
+//  Copyright Eric Niebler 2013-present
+//
+//  Use, modification and distribution is subject to the
+//  Boost Software License, Version 1.0. (See accompanying
+//  file LICENSE_1_0.txt or copy at
+//  http://www.boost.org/LICENSE_1_0.txt)
+//
+// Project home: https://github.com/ericniebler/range-v3
+//
+
+#include <chrono>
+#include <iostream>
+#include <range/v3/all.hpp>
+
+using namespace ranges;
+
+int
+main()
+{
+    // Define an infinite range containing all the Pythagorean triples:
+    auto triples = views::for_each(views::iota(1), [](int z) {
+        return views::for_each(views::iota(1, z + 1), [=](int x) {
+            return views::for_each(views::iota(x, z + 1), [=](int y) {
+                return yield_if(x * x + y * y == z * z,
+                                std::make_tuple(x, y, z));
+            });
+        });
+    });
+
+    //// This alternate syntax also works:
+    // auto triples = iota(1)      >>= [] (int z) { return
+    //                iota(1, z+1) >>= [=](int x) { return
+    //                iota(x, z+1) >>= [=](int y) { return
+    //    yield_if(x*x + y*y == z*z,
+    //        std::make_tuple(x, y, z)); };}; };
+
+    // Display the first 100 triples
+    RANGES_FOR(auto triple, triples | views::take(100))
+    {
+        std::cout << '(' << std::get<0>(triple) << ',' << std::get<1>(triple)
+                  << ',' << std::get<2>(triple) << ')' << '\n';
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////////////////////////
+//  Benchmark Code
+////////////////////////////////////////////////////////////////////////////////////////////////////
+
+class timer
+{
+private:
+    std::chrono::high_resolution_clock::time_point start_;
+
+public:
+    timer()
+    {
+        reset();
+    }
+    void reset()
+    {
+        start_ = std::chrono::high_resolution_clock::now();
+    }
+    std::chrono::milliseconds elapsed() const
+    {
+        return std::chrono::duration_cast<std::chrono::milliseconds>(
+            std::chrono::high_resolution_clock::now() - start_);
+    }
+    friend std::ostream &operator<<(std::ostream &sout, timer const &t)
+    {
+        return sout << t.elapsed().count() << "ms";
+    }
+};
+
+void
+benchmark()
+{
+    // Define an infinite range containing all the Pythagorean triples:
+    auto triples = views::for_each(views::iota(1), [](int z) {
+        return views::for_each(views::iota(1, z + 1), [=](int x) {
+            return views::for_each(views::iota(x, z + 1), [=](int y) {
+                return yield_if(x * x + y * y == z * z,
+                                std::make_tuple(x, y, z));
+            });
+        });
+    });
+
+    static constexpr int max_triples = 3000;
+
+    timer t;
+    int result = 0;
+    RANGES_FOR(auto triple, triples | views::take(max_triples))
+    {
+        int i, j, k;
+        std::tie(i, j, k) = triple;
+        result += (i + j + k);
+    }
+    std::cout << t << '\n';
+    std::cout << result << '\n';
+
+    result = 0;
+    int found = 0;
+    t.reset();
+    for(int z = 1;; ++z)
+    {
+        for(int x = 1; x <= z; ++x)
+        {
+            for(int y = x; y <= z; ++y)
+            {
+                if(x * x + y * y == z * z)
+                {
+                    result += (x + y + z);
+                    ++found;
+                    if(found == max_triples)
+                        goto done;
+                }
+            }
+        }
+    }
+done:
+    std::cout << t << '\n';
+    std::cout << result << '\n';
+}