forked from boostorg/algorithm
124 lines
3.8 KiB
C++
124 lines
3.8 KiB
C++
/*
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Copyright (c) Alexander Zaitsev <zamazan4ik@gmail.com>, 2016
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Distributed under the Boost Software License, Version 1.0. (See
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accompanying file LICENSE_1_0.txt or copy at
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http://www.boost.org/LICENSE_1_0.txt)
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See http://www.boost.org/ for latest version.
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*/
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/// \file is_palindrome.hpp
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/// \brief Checks the input sequence on palindrome.
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/// \author Alexander Zaitsev
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#ifndef BOOST_ALGORITHM_IS_PALINDROME_HPP
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#define BOOST_ALGORITHM_IS_PALINDROME_HPP
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#include <iterator>
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#include <boost/range/begin.hpp>
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#include <boost/range/end.hpp>
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namespace boost { namespace algorithm {
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/// \fn is_palindrome ( BidirectionalIterator begin, BidirectionalIterator end, Predicate p )
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/// \return true if the entire sequence is palindrome
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///
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/// \param begin The start of the input sequence
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/// \param end One past the end of the input sequence
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/// \param p A predicate used to compare the values.
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///
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/// \note This function will return true for empty sequences and for palindromes.
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/// For other sequences function will return false.
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/// Complexity: O(N).
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template <typename BidirectionalIterator, typename Predicate>
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bool is_palindrome(BidirectionalIterator begin, BidirectionalIterator end, Predicate p)
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{
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if(begin == end)
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{
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return true;
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}
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--end;
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while(begin != end)
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{
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if(!p(*begin, *end))
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{
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return false;
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}
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++begin;
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if(begin == end)
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{
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break;
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}
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--end;
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}
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return true;
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}
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/// \fn is_palindrome ( BidirectionalIterator begin, BidirectionalIterator end )
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/// \return true if the entire sequence is palindrome
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///
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/// \param begin The start of the input sequence
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/// \param end One past the end of the input sequence
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///
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/// \note This function will return true for empty sequences and for palindromes.
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/// For other sequences function will return false.
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/// Complexity: O(N).
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template <typename BidirectionalIterator>
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bool is_palindrome(BidirectionalIterator begin, BidirectionalIterator end)
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{
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return is_palindrome(begin, end,
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std::equal_to<typename std::iterator_traits<BidirectionalIterator>::value_type> ());
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}
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/// \fn is_palindrome ( const R& range )
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/// \return true if the entire sequence is palindrome
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///
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/// \param range The range to be tested.
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///
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/// \note This function will return true for empty sequences and for palindromes.
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/// For other sequences function will return false.
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/// Complexity: O(N).
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template <typename R>
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bool is_palindrome(const R& range)
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{
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return is_palindrome(boost::begin(range), boost::end(range));
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}
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/// \fn is_palindrome ( const R& range, Predicate p )
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/// \return true if the entire sequence is palindrome
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///
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/// \param range The range to be tested.
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/// \param p A predicate used to compare the values.
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///
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/// \note This function will return true for empty sequences and for palindromes.
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/// For other sequences function will return false.
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/// Complexity: O(N).
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template <typename R, typename Predicate>
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bool is_palindrome(const R& range, Predicate p)
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{
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return is_palindrome(boost::begin(range), boost::end(range), p);
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}
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//Disable is_palindrome for const char* because it work not properly.
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//Please use string_view for const char* cases.
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//Here we use dirty hack to disable 'is_palindrome' with 'const char*'
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//URL: http://stackoverflow.com/questions/14637356/static-assert-fails-compilation-even-though-template-function-is-called-nowhere
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template<typename T>
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struct foobar : std::false_type
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{ };
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template<typename T = int>
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bool is_palindrome(const char* str)
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{
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static_assert(foobar<T>::value, "Using 'is_palindrome' for 'const char*' is dangerous, because result is always false"
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"(reason: '\0' in the end of the string). You can use string_view in this case");
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return false;
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}
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}}
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#endif // BOOST_ALGORITHM_IS_PALINDROME_HPP
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