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<HTML><HEAD><TITLE>14.3 Partial Sort</TITLE></HEAD><BODY><A HREF="ug1.htm"><IMG SRC="images/banner.gif"></A><BR><A HREF="sor_5132.htm"><IMG SRC="images/prev.gif"></A><A HREF="booktoc1.htm"><IMG SRC="images/toc.gif"></A><A HREF="tindex1.htm"><IMG SRC="images/tindex.gif"></A><A HREF="nth_1433.htm"><IMG SRC="images/next.gif"></A><BR><STRONG>Click on the banner to return to the user guide home page.</STRONG><H2>14.3 Partial Sort</H2><A NAME="idx170"><!></A><P>The generic algorithm <SAMP>partial_sort()</SAMP> sorts only a portion of a sequence. In the first version of the algorithm, three iterators are used to describe the beginning, middle, and end of a sequence. If <SAMP>n</SAMP> represents the number of elements between the start and middle, then the smallest <SAMP>n</SAMP> elements will be moved into this range in order. The remaining elements are moved into the second region. The order of the elements in this second region is undefined.</P><PRE>void partial_sort (RandomAccessIterator first, RandomAccessIterator middle, RandomAccessIterator last [ , Compare ]);</PRE><P>A second version of the algorithm leaves the input unchanged. The output area is described by a pair of random access iterators. If <SAMP>n</SAMP> represents the size of this area, then the smallest <SAMP>n</SAMP> elements in the input are moved into the output in order. If <SAMP>n</SAMP> is larger than the input, then the entire input is sorted and placed in the first <SAMP>n</SAMP> locations in the output. In either case the end of the output sequence is returned as the result of the operation.</P><PRE>RandomAccessIterator partial_sort_copy (InputIterator first, InputIterator last, RandomAccessIterator result_first, RandomAccessIterator result_last [, Compare ] );</PRE><P>Because the input to this version of the algorithm is specified only as a pair of input iterators, the <SAMP>partial_sort_copy()</SAMP> algorithm can be used with any of the containers in the standard library. In the example program it is used with a <A HREF="../stdlibcr/lis_3222.htm"><B><I>list</I></B></A>.</P><PRE>void partial_sort_example () // illustrate the use of the partial sort algorithm{ // make a vector of 15 random integers vector<int> aVec(15); generate (aVec.begin(), aVec.end(), randomValue); // partial sort the first seven positions partial_sort (aVec.begin(), aVec.begin() + 7, aVec.end()); // make a list of random integers list<int> aList(15, 0); generate (aList.begin(), aList.end(), randomValue); // sort only the first seven elements vector<int> start(7); partial_sort_copy (aList.begin(), aList.end(), start.begin(), start.end(), greater<int>());}</PRE><HR><A HREF="sor_5132.htm"><IMG SRC="images/prev.gif"></A> <A HREF="booktoc1.htm"><IMG SRC="images/toc.gif"></A><A HREF="tindex1.htm"><IMG SRC="images/tindex.gif"></A><A HREF="nth_1433.htm"><IMG SRC="images/next.gif"></A><P>©Copyright 1996, Rogue Wave Software, Inc.</P></BODY></HTML>⌨️ 快捷键说明
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