Library: Algorithms
Function
An algorithm that converts a heap into a sorted collection
#include <algorithm> namespace std { template <class RandomAccessIterator> void sort_heap(RandomAccessIterator start, RandomAccessIterator finish); template <class RandomAccessIterator, class Compare> void sort_heap(RandomAccessIterator start, RandomAccessIterator finish, Compare comp); }
A heap is a particular organization of elements in a range between two random access iterators [a, b). Its two key properties are:
*a is the largest element in the range.
*a may be removed by pop_heap() or a new element may be added by push_heap(), in O(logN) time.
These properties make heaps useful as priority queues.
The sort_heap() algorithm converts a heap into a sorted collection over the range [start, finish) using either operator<() or the function object comp. Note that sort_heap() is not stable; equivalent elements are not guaranteed to remain in the same relative order after sort_heap() is applied.
sort_heap() performs approximately N * log(N) comparisons, where N is equal to finish - start.
// // heap_ops.cpp // #include <algorithm> // for copy, make_heap, pop_heap, // and push_heap #include <functional> // for less #include <iostream> // for cout #include <iterator> // for ostream_iterator #include <vector> // for vector template <class charT, class Traits, class T, class Allocator> void print_vector (std::basic_ostream<charT, Traits> &strm, const std::vector<T, Allocator> &v) { std::copy (v.begin (), v.end (), std::ostream_iterator<T, charT, Traits> (strm, " ")); strm << std::endl; } int main () { typedef std::vector<int, std::allocator<int> > Vector; const Vector::value_type d1[] = { 1, 2, 3, 4 }; const Vector::value_type d2[] = { 1, 3, 2, 4 }; // Set up two vectors. Vector v1 (d1 + 0, d1 + sizeof d1 / sizeof *d1); Vector v2 (d2 + 0, d2 + sizeof d2 / sizeof *d2); // Make heaps. std::make_heap (v1.begin (), v1.end ()); std::make_heap (v2.begin (), v2.end (), std::less<int>()); // v1 = (4, x, y, z) and v2 = (4, x, y, z) // Note that x, y and z represent the remaining values // in the container (other than 4). The definition of // the heap and heap operations does not require any // particular ordering of these values. // Copy both vectors to cout. print_vector (std::cout, v1); print_vector (std::cout, v2); // Now let's pop. std::pop_heap (v1.begin (), v1.end ()); std::pop_heap (v2.begin (), v2.end (), std::less<int>()); print_vector (std::cout, v1); print_vector (std::cout, v2); // And push. std::push_heap (v1.begin (), v1.end ()); std::push_heap (v2.begin (), v2.end (), std::less<int>()); print_vector (std::cout, v1); print_vector (std::cout, v2); // Now sort those heaps. std::sort_heap (v1.begin (), v1.end ()); std::sort_heap (v2.begin (), v2.end (), std::less<int>()); print_vector (std::cout, v1); print_vector (std::cout, v2); return 0; } Program Output:
4 2 3 1 4 3 2 1 3 2 1 4 3 1 2 4 4 3 1 2 4 3 2 1 1 2 3 4 1 2 3 4
make_heap(), pop_heap(), push_heap()
ISO/IEC 14882:1998 -- International Standard for Information Systems -- Programming Language C++, Section 25.3.6.4