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182 lines
7.4 KiB
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<HTML>
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<HEAD>
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<TITLE>push_heap()</TITLE>
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<LINK REL=StyleSheet HREF="../rw.css" TYPE="text/css" TITLE="Apache stdcxx Stylesheet"></HEAD>
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<BODY BGCOLOR=#FFFFFF>
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<A HREF="ptr-fun.html"><IMG SRC="images/bprev.gif" WIDTH=20 HEIGHT=21 ALT="Previous file" BORDER=O></A><A HREF="noframes.html"><IMG SRC="images/btop.gif" WIDTH=56 HEIGHT=21 ALT="Top of Document" BORDER=O></A><A HREF="booktoc.html"><IMG SRC="images/btoc.gif" WIDTH=56 HEIGHT=21 ALT="Contents" BORDER=O></A><A HREF="tindex.html"><IMG SRC="images/bindex.gif" WIDTH=56 HEIGHT=21 ALT="Index page" BORDER=O></A><A HREF="queue-h.html"><IMG SRC="images/bnext.gif" WIDTH=25 HEIGHT=21 ALT="Next file" BORDER=O></A><DIV CLASS="DOCUMENTNAME"><B>Apache C++ Standard Library Reference Guide</B></DIV>
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<H2>push_heap()</H2>
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<P><B>Library:</B> <A HREF="2-9.html">Algorithms</A></P>
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<PRE><HR><B><I>Function</I></B><HR></PRE>
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<UL>
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<LI><A HREF="#sec1">Local Index</A></LI>
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<LI><A HREF="#sec2">Summary</A></LI>
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<LI><A HREF="#sec3">Synopsis</A></LI>
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<LI><A HREF="#sec4">Description</A></LI>
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<LI><A HREF="#sec5">Complexity</A></LI>
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<LI><A HREF="#sec6">Example</A></LI>
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<LI><A HREF="#sec7">See Also</A></LI>
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<LI><A HREF="#sec8">Standards Conformance</A></LI>
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</UL>
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<A NAME="sec1"><H3>Local Index</H3></A>
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No Entries
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<A NAME="sec2"><H3>Summary</H3></A>
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<P>An algorithm that places a new element into a heap</P>
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<A NAME="sec3"><H3>Synopsis</H3></A>
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<PRE>#include <algorithm>
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namespace std {
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template <class RandomAccessIterator>
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void
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push_heap(RandomAccessIterator start,
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RandomAccessIterator finish);
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template <class RandomAccessIterator, class Compare>
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void
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push_heap(RandomAccessIterator start,
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RandomAccessIterator finish, Compare comp);
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}
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</PRE>
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<A NAME="sec4"><H3>Description</H3></A>
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<P>A heap is a particular organization of elements in a range between two random access iterators <SAMP>[a, b)</SAMP>. Its two key properties are:</P>
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<OL>
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<LI><P CLASS="LIST"><SAMP>*a</SAMP> is the largest element in the range.</P></LI>
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<LI><P CLASS="LIST"><SAMP>*a</SAMP> may be removed by the <SAMP><A HREF="pop-heap.html">pop_heap()</A></SAMP> algorithm, or a new element may be added by the <SAMP>push_heap()</SAMP> algorithm, in <SAMP>O(logN)</SAMP> time.</P></LI>
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</OL>
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<P>These properties make heaps useful as priority queues.</P>
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<P>The first overload of the <SAMP>push_heap()</SAMP> algorithm uses <SAMP>operator<()</SAMP> for comparison. The second overload uses the supplied binary predicate <SAMP>comp</SAMP>.</P>
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<P>The <SAMP>push_heap()</SAMP> algorithm is used to add a new element to the heap. First, a new element for the heap is added to the end of a range. The <SAMP>push_heap()</SAMP> algorithm assumes that the range <SAMP>[start, finish - 1)</SAMP> is a valid heap. Then it properly positions the element in the location <SAMP>finish - 1</SAMP> into its proper position in the heap, resulting in a heap over the range <SAMP>[start, finish)</SAMP>.</P>
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<A NAME="sec5"><H3>Complexity</H3></A>
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<P>For <SAMP>push_heap()</SAMP> at most <SAMP>log(finish - start)</SAMP> comparisons are performed.</P>
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<A NAME="sec6"><H3>Example</H3></A>
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<UL><PRE>//
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// heap_ops.cpp
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//
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#include <algorithm> // for copy, make_heap, pop_heap,
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// and push_heap
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#include <functional> // for less
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#include <iostream> // for cout
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#include <iterator> // for ostream_iterator
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#include <vector> // for vector
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template <class charT, class Traits, class T, class Allocator>
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void print_vector (std::basic_ostream<charT, Traits> &strm,
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const std::vector<T, Allocator> &v)
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{
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std::copy (v.begin (), v.end (),
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std::ostream_iterator<T, charT, Traits>
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(strm, " "));
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strm << std::endl;
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}
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int main ()
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{
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typedef std::vector<int, std::allocator<int> > Vector;
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const Vector::value_type d1[] = { 1, 2, 3, 4 };
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const Vector::value_type d2[] = { 1, 3, 2, 4 };
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// Set up two vectors.
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Vector v1 (d1 + 0, d1 + sizeof d1 / sizeof *d1);
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Vector v2 (d2 + 0, d2 + sizeof d2 / sizeof *d2);
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// Make heaps.
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std::make_heap (v1.begin (), v1.end ());
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std::make_heap (v2.begin (), v2.end (), std::less<int>());
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// v1 = (4, x, y, z) and v2 = (4, x, y, z)
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// Note that x, y and z represent the remaining values
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// in the container (other than 4). The definition of
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// the heap and heap operations does not require any
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// particular ordering of these values.
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// Copy both vectors to cout.
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print_vector (std::cout, v1);
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print_vector (std::cout, v2);
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// Now let's pop.
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std::pop_heap (v1.begin (), v1.end ());
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std::pop_heap (v2.begin (), v2.end (), std::less<int>());
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print_vector (std::cout, v1);
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print_vector (std::cout, v2);
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// And push.
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std::push_heap (v1.begin (), v1.end ());
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std::push_heap (v2.begin (), v2.end (), std::less<int>());
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print_vector (std::cout, v1);
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print_vector (std::cout, v2);
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// Now sort those heaps.
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std::sort_heap (v1.begin (), v1.end ());
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std::sort_heap (v2.begin (), v2.end (), std::less<int>());
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print_vector (std::cout, v1);
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print_vector (std::cout, v2);
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return 0;
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}
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Program Output:
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</PRE></UL>
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<UL><PRE>4 2 3 1
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4 3 2 1
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3 2 1 4
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3 1 2 4
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4 3 1 2
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4 3 2 1
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1 2 3 4
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1 2 3 4
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</PRE></UL>
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<A NAME="sec7"><H3>See Also</H3></A>
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<P><SAMP><A HREF="make-heap.html">make_heap()</A></SAMP>, <SAMP><A HREF="pop-heap.html">pop_heap()</A></SAMP>, <SAMP><A HREF="sort-heap.html">sort_heap()</A></SAMP></P>
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<A NAME="sec8"><H3>Standards Conformance</H3></A>
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<P><I>ISO/IEC 14882:1998 -- International Standard for Information Systems -- Programming Language C++, Section 25.3.6.1</I></P>
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<BR>
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<HR>
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