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  1. #include <iostream>
  2. #include <vector>
  3. #include <algorithm>
  4. #include <numeric>
  5. #include <random>
  6. #include <chrono>
  7. using namespace std;
  8.  
  9. auto vandenman(const vector<int>& x, const int k) {
  10.     auto y = x;
  11.     std::nth_element(y.begin(), y.begin() + k, y.end());
  12.     const auto kthValue = y[k];
  13.     auto idxK = std::find(x.begin(), x.end(), kthValue);
  14.     return idxK;
  15. }
  16.  
  17. template<typename It>
  18. auto miscco(It first, It last, const int k) {
  19.     auto cmp_it_values = [](It lt, It rt){ return *lt < *rt;};
  20. 	vector<It> y;
  21. 	y.reserve(std::distance(first, last));
  22. 	for(auto it = first; it != last; ++it){
  23. 		y.emplace_back(it);
  24. 	}
  25.     std::nth_element(y.begin(), y.begin() + k, y.end(), cmp_it_values);
  26.     return y[k];
  27. }
  28.  
  29. template<typename It>
  30. It min_k(It first, It last, int k){
  31.    auto cmp_it_values = [](It lt, It rt){ return *lt < *rt;};
  32.    auto max_copy = std::min<long>(k, std::distance(first, last));
  33.    auto start_it = first;
  34.    std::advance(start_it, max_copy);
  35.  
  36. 	k++; // k == 0 has to return smallest one element.
  37.     std::vector<It> k_smallest;
  38.     k_smallest.reserve(k+1);
  39.     for(auto it = first; it != start_it; ++it){
  40.     	k_smallest.push_back(it);
  41.     }
  42.     std::sort(k_smallest.begin(), k_smallest.end(), cmp_it_values);
  43.  
  44.     for(auto it = start_it; it != last; ++it){
  45.         if(k_smallest.empty() || *it < *k_smallest.back()){
  46.             auto insertion_point = std::lower_bound(k_smallest.begin(), k_smallest.end(), 
  47.                                                     it, cmp_it_values);
  48.             k_smallest.insert(insertion_point, it);
  49.             if(k_smallest.size() > k){
  50.                 k_smallest.pop_back(); // Remove the largest value
  51.             }
  52.         }
  53.     }    
  54.     return k_smallest.back(); // The iterator to the min(k, n) smallest value 
  55. }
  56.  
  57.  
  58. template<typename It>
  59. It min_k_heap(It first, It last, int k){
  60. 	k++; // k == 0 has to return smallest one element.
  61.     auto cmp_it_values = [](It lt, It rt){ return *lt < *rt;};
  62.     auto max_copy = std::min<long>(k, std::distance(first, last));
  63.     auto start_it = first;
  64.     std::advance(start_it, max_copy);
  65.  
  66.     std::vector<It> k_smallest;
  67.     k_smallest.reserve(k+1);
  68.     for(auto it = first; it != start_it; ++it){
  69.     	k_smallest.push_back(it);
  70.     }
  71.     std::make_heap(k_smallest.begin(), k_smallest.end(), cmp_it_values);
  72.  
  73. 	for(auto it = start_it; it != last; ++it){
  74.         if(*it < *k_smallest.front()){
  75.         	k_smallest.push_back(it);
  76.         	push_heap(k_smallest.begin(), k_smallest.end(), cmp_it_values);
  77.        	    pop_heap(k_smallest.begin(), k_smallest.end(), cmp_it_values);
  78.        	    k_smallest.pop_back();
  79.         }
  80.     }    
  81.     return k_smallest.front(); // The iterator to the min(k, n) smallest value 
  82. }
  83.  
  84. int main() {
  85.     std::vector<int> v(10000);
  86.     std::vector<std::vector<int>::iterator> vPtr;
  87.     vPtr.reserve(v.size());
  88.     for (auto it = v.begin(); it != v.end(); ++it) {
  89.     	vPtr.push_back(it);
  90.     }
  91.     std::iota (std::begin(v), std::end(v), 0);
  92.     std::mt19937 g(3);
  93.     std::shuffle(v.begin(), v.end(), g);
  94.  
  95. 	{
  96. 	    auto start = chrono::steady_clock::now();
  97. 	    auto ans1 = *vandenman(v, 50);
  98. 	    auto time1 = chrono::steady_clock::now() - start;
  99. 	    cout << "Orig " << ans1<< " time: ";
  100. 	    cout << chrono::duration <double, nano> (time1).count() << " ns" << endl;
  101. 	}
  102. 	{
  103. 	    auto start = chrono::steady_clock::now();
  104. 	    auto ans1 = *miscco(v.begin(), v.end(), 50);
  105. 	    auto time1 = chrono::steady_clock::now() - start;
  106. 	    cout << "Miscco " << ans1<< " time: ";
  107. 	    cout << chrono::duration <double, nano> (time1).count() << " ns" << endl;
  108. 	}
  109. 	{
  110. 		auto start = chrono::steady_clock::now();
  111. 		std::nth_element(vPtr.begin(), std::next(vPtr.begin(), 50), vPtr.end(), [](auto lt, auto rt) { return (*lt) < (*rt); });
  112. 		auto ans1 = **std::next(vPtr.begin(), 50);
  113. 		auto time1 = chrono::steady_clock::now() - start;
  114. 		cout << "Miscco orig " << ans1 << " time: ";
  115. 		cout << chrono::duration <double, nano>(time1).count() << " ns" << endl;
  116. 	}
  117. 	{
  118. 		auto start = chrono::steady_clock::now();
  119. 	    auto ans1 = *min_k(v.begin(), v.end(), 50);
  120. 	    auto time1 = chrono::steady_clock::now() - start;
  121. 	    cout << "Emily Binary insertion " << ans1<< " time: ";
  122. 	    cout << chrono::duration <double, nano> (time1).count() << " ns" << endl;
  123. 	}
  124. 	{
  125. 		auto start = chrono::steady_clock::now();
  126. 	    auto ans1 = *min_k_heap(v.begin(), v.end(), 50);
  127. 	    auto time1 = chrono::steady_clock::now() - start;
  128. 	    cout << "Emily Heap " << ans1<< " time: ";
  129. 	    cout << chrono::duration <double, nano> (time1).count() << " ns" << endl;
  130. 	}
  131.     return 0;
  132. }
Success #stdin #stdout 0s 16072KB
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stdin
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Standard input is empty
stdout
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Orig 50 time: 152499 ns
Miscco 50 time: 173800 ns
Miscco orig 50 time: 115246 ns
Emily Binary insertion 50 time: 72504 ns
Emily Heap 50 time: 65070 ns
https://ideone.com/tLI4dr
language:
C++14 (gcc 8.3)
created:
8 years ago
visibility:
public

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