What's the wrong in this code?

Question

#include <iostream>
#include <string>

std::string dejaVu(std::string);

std::string dejaVu(std::string saisie) {
std::string result;

for (size_t i = 0; i < saisie.size(); i++) {
if (saisie.find_first_of(saisie[i]) != i) {
result = "Deja Vu";
break;
}
else {
result = "Unique";
}
}
return result;
}

int main()
{
std::string str = "sammich";
std::cout << dejaVu(str);

return 0;
}

Answer 1

How? it show 2 test wrong.

Answer 2

It works in PC.
I think there is no problem on it.

Answer 3

Did you consider case with empty input?