c++ - how to use next_permutation

Question

I'm trying to get an arrangement of tic tac toe boards. So I have the following code:

// 5 turns for x if x goes first
std::string moves = "xxxxxoooo";

do {
    std::cout << moves << std::endl;
} while ( std::next_permutation(moves.begin(), moves.end()) );

But it only outputs the original string once. I'm assuming that each character has to be unique. What's a way I can do this?

Answer 1

std::next_permutation returns the next permutation in lexicographic order, and returns false if the first permutation (in that order) is generated.

Since the string you start with ("xxxxxoooo") is actually the last permutation of that string's characters in lexicographic order, your loop stops immediately.

Therefore, you may try sorting moves before starting to call next_permutation() in a loop:

std::string moves = "xxxxxoooo";
sort(begin(moves), end(moves));

while (std::next_permutation(begin(moves), end(moves)))
{
    std::cout << moves << std::endl;
}

Here is a live example.