Standard C++ LibraryCopyright 1996, Rogue Wave Software, Inc.

NAME

  make_heap  - Creates a heap.

SYNOPSIS

  #include <algorithm>

  template <class RandomAccessIterator>
   void
    make_heap(RandomAccessIterator first,
             RandomAccessIterator last);

  template <class RandomAccessIterator, class Compare>
   void
    make_heap(RandomAccessIterator first,
             RandomAccessIterator last, 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:

  1. *a is the largest element in the range.

  2. *a may be removed by the pop_heap algorithm, or a new element can be
       added by the push_heap algorithm, in O(logN) time.

  These properties make heaps useful as priority queues.

  The heap algorithms use less than (operator<) as the default comparison.
  In all of the algorithms, an alternate comparison operator can be
  specified.

  The first version of the make_heap algorithm arranges the elements in the
  range [first, last) into a heap using less than (operator<) to perform
  comparisons.  The second version uses the comparison operator comp to
  perform the comparisons.  Since the only requirements for a heap are the
  two listed above, make_heap is not required to do anything within the range
  (first, last - 1).

COMPLEXITY

  This algorithm makes at most 3 * (last - first)  comparisons.

EXAMPLE

  //
  // heap_ops.cpp
  //
   #include <algorithm>
   #include <vector>
   #include <iostream.h>

  int main(void)
   {
    int d1[4] = {1,2,3,4};
    int d2[4] = {1,3,2,4};

     // Set up two vectors
    vector<int> v1(d1,d1 + 4), v2(d2,d2 + 4);

     // Make heaps
     make_heap(v1.begin(),v1.end());
     make_heap(v2.begin(),v2.end(),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
    ostream_iterator<int,char> out(cout," ");
    copy(v1.begin(),v1.end(),out);
    cout << endl;
    copy(v2.begin(),v2.end(),out);
    cout << endl;

     // Now let's pop
    pop_heap(v1.begin(),v1.end());
    pop_heap(v2.begin(),v2.end(),less<int>());
     // v1 = (3,x,y,4) and v2 = (3,x,y,4)

     // Copy both vectors to cout
    copy(v1.begin(),v1.end(),out);
    cout << endl;
    copy(v2.begin(),v2.end(),out);
    cout << endl;

     // And push
    push_heap(v1.begin(),v1.end());
    push_heap(v2.begin(),v2.end(),less<int>());
     // v1 = (4,x,y,z) and v2 = (4,x,y,z)

     // Copy both vectors to cout
    copy(v1.begin(),v1.end(),out);
    cout << endl;
    copy(v2.begin(),v2.end(),out);
    cout << endl;

     // Now sort those heaps
    sort_heap(v1.begin(),v1.end());
    sort_heap(v2.begin(),v2.end(),less<int>());
     // v1 = v2 = (1,2,3,4)

     // Copy both vectors to cout
    copy(v1.begin(),v1.end(),out);
    cout << endl;
    copy(v2.begin(),v2.end(),out);
    cout << endl;

    return 0;
   }
  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

WARNING

  If your compiler does not support default template parameters then you need
  to always supply the Allocator template argument.  For instance you'll have
  to write:

  vector<int,allocator<int> >

  instead of:

  vector<int>

SEE ALSO

  pop_heap, push_heap and sort_heap

STANDARDS CONFORMANCE

  ANSI X3J16/ISO WG21 Joint C++ Committee



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