generate strings with all permutation of character [closed]

Answer 1

So, I see you are on VC++10:

#include <array>
#include <algorithm>
#include <list>
#include <string>

int main() {

    std::array<char, 24> tAlphabet = {
        'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', // and so on...
    };

    // you could store permutations here, but there will be really, really many of them
    std::list<std::string> tAllPermutations;
    do {
        std::string tCurrentPermutation;

        std::for_each(tAlphabet.begin(), tAlphabet.end(),
            [&tCurrentPermutation] (char tCurrentChar) -> void {
                tCurrentPermutation += tCurrentChar;
        });

        std::cout << tCurrentPermutation << std::endl;
    } while (std::next_permutation(tAlphabet.begin(), tAlphabet.end()));
}

Answer 2

The problem is with your expressions of this form:

(new string *)(c1)

The left hand side isn't a type, it's an expression. When you suffix it with another parenthesized expression it looks like a function call but that only works if the left expression is a function name or function pointer. In this case the new expression has type std::string** which isn't a function pointer.

To construct a temporary string from a single char, you shouldn't use new which dynamically allocates an object; instead you can use a constructor. A suitable one is the one which takes a count and a char to repeat for that count. In your case a count of 1 is what you want:

std::string(1, c1);

You can do something like.

return std::string(1, c1) + std::string(1, c2);

Note that you also don't call generate anywhere and if you do return from the first iteration of a for loop you aren't going to be iterating through all the combinations, you will only every generate the first compination.

Answer 3

I'm quite sure the manual looping can be avoided using std::next_permutation. Manual looping like this is terrible, especially when the Standard library foresees this kind of thing.

Here's some quick code:

#include <algorithm>
    using std::next_permutation;
#include <iostream>
    using std::cout;
    using std::endl;
#include <string>
    using std::string;

int main()
{
    string currentPermutation = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
    size_t i=0;
    do
    {
        cout << "permutation " << i << ": " << currentPermutation << endl;
        ++i;
    } while( next_permutation(currentPermutation.begin(), currentPermutation.end()) );
    return 0;
}

This will permutate through all combinations of the string.

Answer 4

You should use a stringstream to create your string as follows:

stringstream s;
s << c1 << c2 << c3 << c4 << ends;
return s.str();