Find string with the most different characters - c++

Question

I have an array of strings,
sparnus , sapnus , lol , noon ...
As you can see they both start and end with the same character.
What can i do to compare, let's say "sparnus" with "sapnus" and find out which string has more different characters?
sparnus has s p a r n u s (6 different characters)
sapnus has s a p n u s (5 different characters)
(note: s repeats itself, so it's not a different character)
is there a function? algorithm? tips and advice are welcome.

Answer 1

Standard container std::set itself is in fact an algorithm.:)
For example
#include <iostream>
#include <string>
#include <set>
int main()
{
std::string s1( "sparnus" ), s2( "sapnus" );
std::cout << std::set<char>( s1.begin(), s1.end() ).size() << std::endl;
std::cout << std::set<char>( s2.begin(), s2.end() ).size() << std::endl;
return 0;
}
The output is
6
5
So you can use standard algorithm std::max_element with a predicat that compares sizes of two sets built from strings.
Here is an example
#include <iostream>
#include <string>
#include <set>
#include <algorithm>
#include <cstring>
#include <iterator>
int main()
{
const size_t N = 10;
char s[][N] = { "lol" , "noon", "sparnus", "sapnus" };
auto it = std::max_element( std::begin( s ), std::end( s ),
[]( const char *a, const char *b )
{
return std::set<char>( a, a + std::strlen( a ) ).size() <
std::set<char>( b, b + std::strlen( b ) ).size();
} );
std::cout << *it<< std::endl;
return 0;
}
The output is
sparnus
Or you can use the approach that was shown in one post here that was deleted by unknown reason. For example You can sort all words by using standard algorithm std::sort then apply standard algorithm std::unique and standard C function std::strlen will give you the number of unique characters in each string.

Answer 2

template <typename InputIterator>
std::size_t countDiffChars( InputIterator first,
InputIterator last )
{
bool lookup[1 << CHAR_BIT] {};
std::size_t count = 0;
while (first != last)
{
auto&& val = lookup[(unsigned char)*first++];
count += !val;
val = true;
}
return count;
}
Usage:
char const str[] = "Hello";
auto c = countDiffChars(std::begin(s), std::end(s));
Demo.

Answer 3

use a boolean array of 256 entries and loop on the string and set each flag of the array to true indexing by the letter of the string. At the end you may count the number of trues in the array and found how many different characters are there.
If instead of a boolean array you use an int array you may also count how many times a letter is found if that serves somehow! ( that may be done if you don't want to use sets as a previous answer points ).
#include <iostream>
#include <string>
int cnt(std::string s){
bool b[0x100]={false};int r=0;
for(int i:s) b[i]=true;for(int i:b) r+=i;
return r;
}
int main(int argc, char **argv)
{ std::cout<<cnt("sparnus")<<" "<<cnt("sapnus")<<std::endl;
return 0;
}