Library: Algorithms
Function
Templatized algorithm for sorting collections of entities
#include <algorithm> namespace std { template <class InputIterator, class RandomAccessIterator> void partial_sort_copy(InputIterator start, InputIterator finish, RandomAccessIterator result_start, RandomAccessIterator result_finish); template <class InputIterator, class RandomAccessIterator, class Compare> void partial_sort_copy(InputIterator start, InputIterator finish, RandomAccessIterator result_start, RandomAccessIterator result_finish, Compare comp); }
The partial_sort_copy() algorithm places the smaller of finish - start and result_finish - result_start sorted elements from the range [start, finish) into the range beginning at result_start (in other words, the range: [result_start, result_start+min(finish - start, result_finish - result_start)). The effect is as if the range [start,finish) were placed in a temporary buffer, sorted, and then as many elements as possible copied into the range [result_start, result_finish).
The first version of the algorithm uses operator<() as the comparison operator for the sort. The second version uses the function object comp.
partial_sort_copy() does approximately (finish-start) * log(min(finish-start, result_finish-result_start)) comparisons.
// // partsort.cpp // #include <algorithm> // for partial_sort #include <iostream> // for cout, endl #include <iterator> // for ostream_iterator #include <vector> // for vector int main() { typedef std::vector<int, std::allocator<int> > Vector; typedef std::ostream_iterator<int, char, std::char_traits<char> > Iter; const Vector::value_type a[] = { 17, 3, 5, -4, 1, 12, -10, -1, 14, 7, -6, 8, 15, -11, 2, -2, 18, 4, -3, 0 }; Vector v1 (a + 0, a + sizeof a / sizeof *a); // Output original vector. std::cout << "For the vector: "; std::copy (v1.begin (), v1.end (), Iter (std::cout, " ")); // Partial sort the first seven elements. std::partial_sort (v1.begin (), v1.begin () + 7, v1.end ()); // Output result. std::cout << "\n\nA partial_sort of seven elements " << "gives: \n "; std::copy (v1.begin (), v1.end (), Iter (std::cout, " ")); std::cout << std::endl; // A vector of ten elements. Vector v2 (Vector::size_type (10), 0); // Sort the last ten elements in v1 into v2. std::partial_sort_copy (v1.begin () + 10, v1.end (), v2.begin (), v2.end ()); // Output result. std::cout << "\nA partial_sort_copy of the last ten elements " << "gives: \n "; std::copy (v2.begin (), v2.end (), Iter (std::cout, " ")); std::cout << std::endl; return 0; } Program Output: For the vector: 17 3 5 -4 1 12 -10 -1 14 7 -6 8 15 -11 2 -2 18 4 -3 0 A partial_sort of seven elements gives: -11 -10 -6 -4 -3 -2 -1 17 14 12 7 8 15 5 3 2 18 4 1 0 A partial_sort_copy of the last ten elements gives: 0 1 2 3 4 5 7 8 15 18
sort()¸ stable_sort(), partial_sort()
ISO/IEC 14882:1998 -- International Standard for Information Systems -- Programming Language C++, Section 25.3.1.4