Apache C++ Standard Library Reference Guide

## sort_heap()

Library: Algorithms

    Function

- Local Index
- Summary
- Synopsis
- Description
- Complexity
- Example
- See Also
- Standards Conformance

### Local Index

No Entries

### Summary

An algorithm that converts a heap into a sorted collection

### Synopsis

    #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);
    }

### Description

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.

### Complexity

`sort_heap()` performs approximately `N * log(N)` comparisons, where `N` is equal to `finish - start`.

### Example

    //
    //  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

### See Also

`make_heap()`, `pop_heap()`, `push_heap()`

### Standards Conformance

ISO/IEC 14882:1998 -- International Standard for Information Systems -- Programming Language C++, Section 25.3.6.4