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<Head>
<Title>make_heap</Title>
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<H1>make_heap</H1>
<Table CellPadding=0 CellSpacing=0 width=100%>
<TR>
<TD Align=left><Img src = "algorithms.gif" Alt="" WIDTH = "194" HEIGHT = "38" ></TD>
<TD Align=right><Img src = "function.gif" Alt="" WIDTH = "194" HEIGHT = "38" ></TD>
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<TR>
<TD Align=left VAlign=top><b>Category</b>: algorithms</TD>
<TD Align=right VAlign=top><b>Component type</b>: function</TD>
</TR>
</Table>
<h3>Prototype</h3>
<tt>Make_heap</tt> is an overloaded name; there are actually two
<tt>make_heap</tt> functions.
<pre>
template <class <A href="RandomAccessIterator.html">RandomAccessIterator</A>>
void make_heap(RandomAccessIterator first, RandomAccessIterator last);
template <class <A href="RandomAccessIterator.html">RandomAccessIterator</A>, class <A href="StrictWeakOrdering.html">StrictWeakOrdering</A>>
void make_heap(RandomAccessIterator first, RandomAccessIterator last,
StrictWeakOrdering comp);
</pre>
<h3>Description</h3>
<tt>Make_heap</tt> turns the range <tt>[first, last)</tt> into a heap <A href="#1">[1]</A>.
<P>
The two versions of <tt>make_heap</tt> differ in how they define whether one
element is less than another. The first version compares
objects using <tt>operator<</tt>, and the second compares objects using
a <A href="functors.html">function object</A> <tt>comp</tt>.
In the first version the postcondition is that <tt><A href="is_heap.html">is_heap</A>(first, last)</tt>
is <tt>true</tt>, and in the second version the
postcondition is that <tt><A href="is_heap.html">is_heap</A>(first, last, comp)</tt> is <tt>true</tt>.
<h3>Definition</h3>
Defined in the standard header <A href="algorithm">algorithm</A>, and in the nonstandard
backward-compatibility header <A href="algo.h">algo.h</A>.
<h3>Requirements on types</h3>
For the first version:
<UL>
<LI>
<tt>RandomAccessIterator</tt> is a model of <A href="RandomAccessIterator.html">Random Access Iterator</A>.
<LI>
<tt>RandomAccessIterator</tt> is mutable.
<LI>
<tt>RandomAccessIterator</tt>'s value type is a model of <A href="LessThanComparable.html">LessThan Comparable</A>.
<LI>
The ordering on objects of <tt>RandomAccessIterator</tt>'s value type is a <i>strict
weak ordering</i>, as defined in the <A href="LessThanComparable.html">LessThan Comparable</A> requirements.
</UL>
For the second version:
<UL>
<LI>
<tt>RandomAccessIterator</tt> is a model of <A href="RandomAccessIterator.html">Random Access Iterator</A>.
<LI>
<tt>RandomAccessIterator</tt> is mutable.
<LI>
<tt>StrictWeakOrdering</tt> is a model of <A href="StrictWeakOrdering.html">Strict Weak Ordering</A>.
<LI>
<tt>RandomAccessIterator</tt>'s value type is convertible to
<tt>StrictWeakOrdering</tt>'s argument type.
</UL>
<h3>Preconditions</h3>
<UL>
<LI>
<tt>[first, last)</tt> is a valid range.
</UL>
<h3>Complexity</h3>
Linear. At most <tt>3*(last - first)</tt> comparisons.
<h3>Example</h3>
<pre>
int main()
{
int A[] = {1, 4, 2, 8, 5, 7};
const int N = sizeof(A) / sizeof(int);
make_heap(A, A+N);
<A href="copy.html">copy</A>(A, A+N, <A href="ostream_iterator.html">ostream_iterator</A><int>(cout, " "));
cout << endl;
<A href="sort_heap.html">sort_heap</A>(A, A+N);
<A href="copy.html">copy</A>(A, A+N, <A href="ostream_iterator.html">ostream_iterator</A><int>(cout, " "));
cout << endl;
}
</pre>
<h3>Notes</h3>
<P><A name="1">[1]</A>
A heap is a particular way of ordering the elements in a range of
<A href="RandomAccessIterator.html">Random Access Iterators</A> <tt>[f, l)</tt>. The reason heaps are useful
(especially for sorting, or as priority queues) is that they satisfy
two important properties. First, <tt>*f</tt> is the largest element in the
heap. Second, it is possible to add an element to a heap (using
<tt>push_heap</tt>), or to remove <tt>*f</tt>, in logarithmic time.
Internally, a heap is simply a tree represented as a sequential range.
The tree is constructed so that that each
node is less than or equal to its parent node.
<h3>See also</h3>
<tt><A href="push_heap.html">push_heap</A></tt>, <tt><A href="pop_heap.html">pop_heap</A></tt>, <tt><A href="sort_heap.html">sort_heap</A></tt>, <tt><A href="sort.html">sort</A></tt>, <tt><A href="is_heap.html">is_heap</A></tt>
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