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#include <chrono>
#include <vector>
#include <iostream>
#include <algorithm>
#include <string>
#include <thread>
#include <random>
class Measure
{
public:
Measure()
: start(std::chrono::high_resolution_clock::now())
{
}
~Measure()
{
auto end = std::chrono::high_resolution_clock::now();
std::chrono::duration<double> delta = end - start;
std::cout << " " << delta.count() * 1000 << " ms passed" << std::endl;
}
std::chrono::time_point<std::chrono::high_resolution_clock> start{};
};
template<typename Callable>
void measure(const std::string& text, Callable c)
{
std::cout << text << ":\n";
for(int i = 0; i < 3; ++i)
{ // RAII timed scoped
Measure m;
c();
}
}
int main()
{
using namespace std::chrono_literals;
// Sanity check measurement mechanism
measure("Sanity check (sleep 100ms)",
[]()
{
std::this_thread::sleep_for(100ms);
});
// std::find() on a vector<int>:
// Use a vector large enough to get meaningful values on your machine
// (1,000,000 elements are likely not enough). Measure the time needed to
// * Find the 7 in the middle of a vector<int> where all other elements are
// not 7.
{
std::vector<int> v(10'000'000, 42); // one million items with the int 42
v[v.size() / 2] = 7; // set middle item to 7
measure("std::find 7 in the middle",
[&v]()
{
if(std::find(v.begin(), v.end(), 7) == std::end(v))
{
std::cout << "That was unexpected!\n";
}
});
}
// * Try to find a 7 in a vector<int> where no element is 7
{
std::vector<int> v(10'000'000, 42); // one million items with the int 42
measure("std::find 7 not there",
[&v]()
{
if(std::find(v.begin(), v.end(), 7) != std::end(v))
{
std::cout << "That was unexpected!\n";
}
});
}
// std::find_if() on a vector<int>:
// Use a vector large enough to get meaningful values on your machine.
// Measure the time needed to
// * Find the x < 7 in the middle of a vector<int> where all other elements
// are >= 7.
{
std::vector<int> v(10'000'000, 42); // one million items with the int 42
v[v.size() / 2] = 5; // set middle item to 5
measure("std::find_if x < 7 in the middle",
[&v]()
{
if(std::find_if(v.begin(), v.end(), [](int x){ return x < 7;}) == std::end(v))
{
std::cout << "That was unexpected!\n";
}
});
}
// * Try to find an x < 7 in a vector<int> where all elements are >= 7.
{
std::vector<int> v(10'000'000, 42); // one million items with the int 42
measure("std::find_if x < 7 not there",
[&v]()
{
if(std::find_if(v.begin(), v.end(), [](int x){ return x < 7;}) != std::end(v))
{
std::cout << "That was unexpected!\n";
}
});
}
// std::find() on a vector<std::string>:
// Generate a vector<string> containing 1,000,000 random 20-letter strings
// (don't bother timing this).
{
std::default_random_engine generator;
// Randomly generate characters from the range [A;Z]
std::uniform_int_distribution<char> distrib('A', 'Z');
std::vector<std::string> vs;
vs.resize(10'000'000);
for(auto &str: vs)
{
str.reserve(20);
for(auto i = 0u; i < str.capacity(); ++i)
{
str += distrib(generator);
}
}
std::string needle(20, 'X');
// Measure the time needed to
// * Try to find XXXXXXXXXXXXXXXXXXXX (20 Xs) in that vector using
// std::find().
measure("Find " + needle + " (not there)",
[&]()
{
if(std::find(vs.begin(), vs.end(), needle) != std::end(vs))
{
std::cout << "That was unexpected!\n";
}
});
// * Was it there? Unlikely, but if so, try with another value.
// Alternatively (optional), ensure you never generate
// XXXXXXXXXXXXXXXXXXXX in the first place.
//
// * Place XXXXXXXXXXXXXXXXXXXX (or whatever value is not present) in the
// middle and find it using std::find().
vs[vs.size() / 2] = needle;
measure("Find " + needle + " (in the middle)",
[&]()
{
if(std::find(vs.begin(), vs.end(), needle) == std::end(vs))
{
std::cout << "That was unexpected!\n";
}
});
}
}
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