#include <iostream>
#include <algorithm>
#include <array>
#include <string>
#include <climits>
 
std::string change(std::string str)
{
    std::string alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";
    std::string keyboard = "AZERTYUIOPQSDFGHJKLMWXCVBNazertyuiopqsdfghjklmwxcvbn";
 
    // setup transformation array.
    std::array<char, 1 << CHAR_BIT> xform;
    xform.fill('.');
    for (auto it = alphabet.begin(); it!= alphabet.end(); ++it)
        xform[ static_cast<unsigned char>(*it)] = keyboard[it-alphabet.begin()];
 
    std::transform(str.begin(), str.end(), str.begin(),
       [&xform](char c) { return xform[static_cast<unsigned char>(c)];});
 
    return str;
}
 
int main()
{
    std::cout << change("Hello") << '\n';
}

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