To the readers: I had to use ::tolower because the std:: version was causing compiler errors. I'm investigating this right now. The issue stems from std::tolower being overloaded. What is funny is that it is in header <locale>, which means that the standard library implementation includes it in some way. Rakete1111 proposed lambda version, which works great.
Yes.
Use more standard library:
The std::string provides reverse iterators, so there is no need to do any copy at all. In fact, it is possible to it with indices, but it won't look that pretty:
return std::equal(str.cbegin(), str.cbegin() + str.size() / 2, str.crbegin(),
[](unsigned char lhs, unsigned char rhs) {
return std::tolower(lhs) == std::tolower(rhs);
});
The actual version was different, thanks to Rakete1111 for a new version. There is a note in the comments from Loki and Jerry: it seems like using functions in <cctype> are dangerous and will result in undefined behavior unless the input is cast into unsigned char first.
It is also possible to refactor the ugly + str.size() / 2 into reusable function:
#include <iterator>
//some namespace
template <typename Container>
constexpr auto mid(const Container& container)
{
auto half_distance = std::distance(std::begin(container),
std::end(container)) / 2;
return std::next(container.begin(), half_distance);
}
Then it transforms into:
bool is_palindrome(const std::string& str) {
return std::equal(str.cbegin(), mid(str), str.crbegin(),
[](unsigned char lhs, unsigned char rhs) {
return std::tolower(lhs) == std::tolower(rhs);
});
}
Other things that could be done better:
Avoid std::endl. It can cause big performance issues.
There is a typo in the word palindrome.
std::boolalpha could be used to provide more user friendly output.
more unit tests.
It seems like the code is missing <cctype> header as well.
putting everything into a namespace. Absence of it will force users to do unqualified call, which is prone to ADL, which is sometimes very evil.
Put together:
#include <iomanip>
#include <iostream>
#include <algorithm>
#include <string>
#include <cctype>
#include <iterator>
//some namespace
template <typename Container>
constexpr auto mid(const Container& container)
{
auto half_distance = std::distance(std::begin(container),
std::end(container)) / 2;
return std::next(container.begin(), half_distance);
}
bool is_palindrome(const std::string& str) {
return std::equal(str.cbegin(), mid(str), str.crbegin(),
[](unsigned char lhs, unsigned char rhs) {
return std::tolower(lhs) == std::tolower(rhs);
});
}
int main()
{
std::string str{ "KArak" };
std::cout << std::boolalpha;
std::cout << "is \"KArak\" palindrome? " << is_palindrome(str) << '\n';
std::cout << "is \"fuf\" palindrome? " << is_palindrome("fuf") << '\n';
std::cout << "is empty string palindrome? " << is_palindrome("") << '\n';
return 0;
}
Live demo.
