Every permutation of the alphabet up to 29 characters?

Question

I\'m attempting to write a program that will generate a text file with every possible permutation of the alphabet from one character up to twenty-nine characters. I\'ve chosen 2

Answer 1

Here is a simple untested program in C++ that creates the words by counting in Base 26:

#include 
#include 

int main(void)
{
    //----------------------------------------------------------
    //  Print permuations of strings of letters up to length 5.
    //  Use base 26 arithmetic.
    //----------------------------------------------------------
    const unsigned int MAX_ITERATIONS = 26 * 26 * 26 * 26 * 26;

    std::string word = "A";
    for (unsigned int i = 0; i < MAX_ITERATIONS; ++i)
    {
        //------------------------------------------------------
        //  Print the word
        //------------------------------------------------------
        std::cout << word << std::endl;

        //------------------------------------------------------
        //  Increment the word, using base 26 arithmetic.
        //  A, B, C, ..., Z.
        //  AA, BA, CA, ..., ZA, AB, BB, CB, DB, ..., ZZ.
        //  AAA, BAA, CAA, ..., ZAA, ABA, BBA, CBA, DBA, ..., ZZZ.
        //------------------------------------------------------
        bool            carry_generated = false;
        unsigned int    digit = 0;
        do
        {
            carry_generated = false;
            if (word[digit] < 'Z')
            {
                ++word[digit];
                break;
            }
            word[digit++] = 'A';
            if (word.length() == digit)
            {
                word += "A";
                break;
            }
            carry_generated = true;
        } while (carry_generated && (digit < 5));
    }

    return 0;
}

The number of words printed can be reduced by checking a word list (a.k.a. dictionary) before printing. If the word is in the word list, print it.

The biggest issue with a word length of 29 is representing the quantity. The quantity overflows the range of the standard C++ unsigned integers. A Big Int library would need to be used. The next issue is the time required to process every combination. Multiply the quantity by 1 microsecond per iteration (a kind of worse case) and reduce down to days, hours, minutes and seconds. Perhaps years may be required.