bool
recursive_binary_search (int *array, int max, int min, int value) //O(1)?O(n)?
{
if (max < min)
return false;
int mid = (max + min) / 2;
if (value == array[mid])
return true;
if (value > array[mid])
return recursive_binary_search (array, max, mid+1, value);
else
return recursive_binary_search (array, mid-1, min, value);
}
int recursive_binary_search(const std::vector<int>& vec, int begin, int end, const int key)
{
if (begin < end) {
int mid = (begin + end) / 2;
if (key == vec[mid]) {
return mid;
} else if (key < vec[mid]) {
return recursive_binary_search(vec, begin, mid - 1, key);
}
return recursive_binary_search(vec, mid + 1, end, key);
}
if (begin == end && key == vec[begin]) {
return begin;
}
return -1;
}
bool
recursive (int* array, int size, int value)//if not found,it always return 4. why? //O(log n)
{
if (NULL == array || size <= 0)
return false;
int min = 0;
int max = size - 1;
return recursive_binary_search (array, max, min, value);
}
int main(int argc, char** argv) {
if(argc != 2) {
std::cerr << "Usage: " << argv[0] << " <filename>\n";
return 1;
}
std::vector<unsigned> vec;
std::ofstream times_file{argv[1]};
std::mt19937_64 gen{std::random_device{}()};
while (vec.size() < config::max_elements) {
{
std::uniform_int_distribution<unsigned> dist{1, 4};
unsigned tmp = (vec.empty() ? 0 : vec.back()) + dist(gen);
for(std::size_t i = 0; i < config::step; ++i) {
tmp += dist(gen);
vec.push_back(tmp);
}
}
const auto elements = vec.size();
std::cout << "n=" << elements << std::endl;
times_file << elements;
// don't take the middle one, since all binary searches would be constant then:
const auto value = elements > 2 ? vec.at(1 + elements/2) : vec.front();
// In order to prevent wrong meassurments due to cache-effects always switch between
// a linear and a binary search.
//
// Also: the enforces are needed in order to prevent the compiler from completely
// optimizing away the searches.
{
auto before = std::chrono::high_resolution_clock::now();
auto it = iterative_binary_search(vec.begin(), vec.end(), value);
auto after = std::chrono::high_resolution_clock::now();
enforce(it != vec.end(), "iterative binary search");
times_file << " " << time_diff(before, after);
}
{
auto before = std::chrono::high_resolution_clock::now();
auto it = linear_search(vec.begin(), vec.end(), value);
auto after = std::chrono::high_resolution_clock::now();
enforce(it != vec.end(), "linear search");
times_file << " " << time_diff(before, after);
}
{
auto before = std::chrono::high_resolution_clock::now();
auto it = recursive_binary_search(vec.begin(), vec.end(), value);
auto after = std::chrono::high_resolution_clock::now();
enforce(it != vec.end(), "recursive binary search");
times_file << " " << time_diff(before, after);
}
{
auto before = std::chrono::high_resolution_clock::now();
auto it = std::find(vec.begin(), vec.end(), value);
auto after = std::chrono::high_resolution_clock::now();
enforce(it != vec.end(), "std::find");
times_file << " " << time_diff(before, after);
}
{
auto before = std::chrono::high_resolution_clock::now();
auto it = std::lower_bound(vec.begin(), vec.end(), value);
auto after = std::chrono::high_resolution_clock::now();
enforce(it != vec.end(), "std::lower_bound");
times_file << " " << time_diff(before, after);
}
times_file << '\n';
}
}
