How to find first recurring character in a string

first_recurring_character.cpp

#include <iostream>
#include <iomanip>
#include <cstdlib>
#include <string>
#include <vector>
#include <array>
#include <utility>
#include <algorithm>
#include <unordered_map>

using Result = std::pair< char, bool >;
const Result findFirstRecurringCharacter( const std::string& s ) noexcept;

int main( void )
{
    const std::vector< std::string > strings
    {
        "ABCDA",
        "ABCDE",
        "ABCBA"
    };

    for ( auto& s : strings )
    {
        auto result = findFirstRecurringCharacter( s );
        std::cout << std::quoted( s ) << '\n'
                  << "Found? "
                  << std::boolalpha << result.second << '\n'
                  << ( result.second ? result.first : '\0' )
                  << "\n\n";
    }

    return EXIT_SUCCESS;
}

const Result findFirstRecurringCharacter( const std::string& s ) noexcept
{
    using LookupTable = std::unordered_map< char, char >;
    LookupTable table;

    for ( auto& c : s )
    {
        if ( table.find( c ) != table.end() )
        {
            return { c, true };
        }

        table[ c ] = c;
    }

    return { '\0', false };
}