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| <H2>next_permutation()</H2> |
| <P><B>Library:</B> <A HREF="2-9.html">Algorithms</A></P> |
| |
| <PRE><HR><B><I>Function</I></B><HR></PRE> |
| |
| <UL> |
| <LI><A HREF="#sec1">Local Index</A></LI> |
| <LI><A HREF="#sec2">Summary</A></LI> |
| <LI><A HREF="#sec3">Synopsis</A></LI> |
| <LI><A HREF="#sec4">Description</A></LI> |
| <LI><A HREF="#sec5">Complexity</A></LI> |
| <LI><A HREF="#sec6">Example</A></LI> |
| <LI><A HREF="#sec7">See Also</A></LI> |
| <LI><A HREF="#sec8">Standards Conformance</A></LI> |
| </UL> |
| <A NAME="sec1"><H3>Local Index</H3></A> |
| No Entries |
| <A NAME="sec2"><H3>Summary</H3></A> |
| <P>Algorithm that generates successive permutations of a sequence based on an ordering function </P> |
| <A NAME="sec3"><H3>Synopsis</H3></A> |
| |
| <PRE>#include <algorithm> |
| |
| namespace std { |
| template <class BidirectionalIterator> |
| bool next_permutation(BidirectionalIterator start, |
| BidirectionalIterator finish); |
| |
| template <class BidirectionalIterator, class Compare> |
| bool next_permutation(BidirectionalIterator start, |
| BidirectionalIterator finish, |
| Compare comp); |
| } |
| </PRE> |
| <A NAME="sec4"><H3>Description</H3></A> |
| <P>The permutation-generating algorithms, <SAMP>next_permutation()</SAMP> and <SAMP><A HREF="prev-permutation.html">prev_permutation()</A></SAMP>, assume that the set of all permutations of the elements in a sequence is lexicographically sorted with respect to <SAMP>operator<()</SAMP> or the binary predicate <SAMP>comp</SAMP>. For example, if a sequence includes the integers 1 2 3, that sequence has six permutations. In order from first to last, they are: 1 2 3, 1 3 2, 2 1 3, 2 3 1, 3 1 2, and 3 2 1. </P> |
| <P>The <SAMP>next_permutation()</SAMP> algorithm takes a sequence defined by the range <SAMP>[start, finish)</SAMP> and transforms it into its next permutation, if possible. If such a permutation does exist, the algorithm completes the transformation and returns <SAMP>true</SAMP>. If the permutation does not exist, <SAMP>next_permutation()</SAMP> transforms the permutation into its "first" permutation and returns <SAMP>false</SAMP>. <SAMP>next_permutation()</SAMP> does the transformation according to the lexicographical ordering defined by either <SAMP>operator<()</SAMP> (used in the first version of the algorithm) or the binary predicate <SAMP>comp</SAMP> (which is user-supplied in the second version of the algorithm). </P> |
| <P>For example, if the sequence defined by <SAMP>[start, finish)</SAMP> contains the integers 3 2 1 (in that order), there is <I>not</I> a "next permutation." Therefore, the algorithm transforms the sequence into its first permutation (1 2 3) and returns <SAMP>false</SAMP>.</P> |
| <A NAME="sec5"><H3>Complexity</H3></A> |
| <P>At most <SAMP>(finish - start)/2 </SAMP>swaps are performed.</P> |
| <A NAME="sec6"><H3>Example</H3></A> |
| |
| <UL><PRE>// |
| // permute.cpp |
| // |
| |
| #include <algorithm> // for next_permutation, prev_permutation |
| #include <functional> // for less |
| #include <iostream> // for cout, endl |
| #include <numeric> // for accumulate |
| #include <vector> // for vector |
| |
| |
| int main () |
| { |
| typedef std::vector<int, std::allocator<int> > IntVec; |
| typedef std::vector<char, std::allocator<char> > CharVec; |
| |
| // Initialize a vector using an array of integers. |
| const IntVec::value_type a1[] = { 0, 0, 0, 0, 1, |
| 0, 0, 0, 0, 0 }; |
| const CharVec::value_type a2[] = "abcdefghji"; |
| |
| // Create the initial set and copies for permuting. |
| IntVec m1 (a1, a1 + sizeof a1 / sizeof *a1); |
| IntVec prev_m1 (10); |
| IntVec next_m1 (10); |
| |
| CharVec m2 (a2, a2 + sizeof a2 / sizeof *a2 - 1); |
| CharVec prev_m2 (10); |
| CharVec next_m2 (10); |
| |
| std::copy (m1.begin (), m1.end (), prev_m1.begin ()); |
| std::copy (m1.begin (), m1.end (), next_m1.begin ()); |
| std::copy (m2.begin (), m2.end (), prev_m2.begin ()); |
| std::copy (m2.begin (), m2.end (), next_m2.begin ()); |
| |
| // Create permutations. |
| typedef std::less<IntVec::value_type> IntLess; |
| typedef std::less<CharVec::value_type> CharLess; |
| |
| std::prev_permutation (prev_m1.begin (), prev_m1.end (), |
| IntLess ()); |
| std::next_permutation (next_m1.begin (), next_m1.end (), |
| IntLess ()); |
| std::prev_permutation (prev_m2.begin (), prev_m2.end (), |
| CharLess ()); |
| std::next_permutation (next_m2.begin (), next_m2.end (), |
| CharLess ()); |
| |
| // Output results. |
| |
| typedef std::ostream_iterator<IntVec::value_type, char, |
| std::char_traits<char> > |
| IntOSIter; |
| |
| typedef std::ostream_iterator<CharVec::value_type, char, |
| std::char_traits<char> > |
| CharOSIter; |
| |
| std::cout << "Example 1: \n Original values: "; |
| std::copy (m1.begin (), m1.end (), |
| IntOSIter (std::cout, " ")); |
| |
| std::cout << "\n Previous permutation: "; |
| std::copy (prev_m1.begin (), prev_m1.end (), |
| IntOSIter (std::cout, " ")); |
| |
| std::cout << "\n Next Permutation: "; |
| std::copy (next_m1.begin (), next_m1.end (), |
| IntOSIter (std::cout, " ")); |
| |
| std::cout << "\n\nExample 2: \n "; |
| << "Original values: "; |
| std::copy (m2.begin (), m2.end (), |
| CharOSIter (std::cout, " ")); |
| |
| std::cout << "\n Previous Permutation: "; |
| std::copy (prev_m2.begin (), prev_m2.end (), |
| CharOSIter (std::cout, " ")); |
| |
| std::cout << "\n Next Permutation: "; |
| std::copy (next_m2.begin (), next_m2.end (), |
| CharOSIter (std::cout, " ")); |
| |
| std::cout << std::endl << std::endl; |
| |
| return 0; |
| } |
| |
| |
| Program Output: |
| </PRE></UL> |
| <UL><PRE>Example 1: |
| Original values: 0 0 0 0 1 0 0 0 0 0 |
| Previous permutation: 0 0 0 0 0 1 0 0 0 0 |
| Next Permutation: 0 0 0 1 0 0 0 0 0 0 |
| |
| Example 2: |
| Original values: a b c d e f g h j i |
| Previous Permutation: a b c d e f g h i j |
| Next Permutation: a b c d e f g i h j |
| |
| </PRE></UL> |
| <A NAME="sec7"><H3>See Also</H3></A> |
| <P><SAMP><A HREF="prev-permutation.html">prev_permutation()</A></SAMP></P> |
| <A NAME="sec8"><H3>Standards Conformance</H3></A> |
| <P><I>ISO/IEC 14882:1998 -- International Standard for Information Systems -- Programming Language C++, Section 25.3.9</I></P> |
| |
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