How to efficiently check if a word's all letters are the same in C++

I have checked and couldn't a better option by checking the word's letters one by one. I've decided to use the ascii equivalence of the letter check by diving the word but didn't lead to any where as well. Any Ideas?


#include <string>

bool are_all_characters_the_same(const std::string &s) {
    return (s.size() == 0) || s.find_first_not_of(s[0]) == std::string::npos;

Clearly in the worst case it can't be done without examining every character. Whichever character(s) you don't examine, might be the same as the others or different, and the result needs to be sensitive to that in the case where the ones you do examine are all the same.

If you know something about what might be in the string, then the order in which you examine the characters might affect how early you can bail out. But knowing nothing, you may as well read them in order, and reading them in order might result in better cache performance.

Things get more complicated if the string is long enough that it's worth parallelizing.

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