Generating all combinations with unknown length - c++

Question

I'm practicing in programming and I generating all combinations in c++. I know how to generate all combination in
certain length
My result is something like that
A A A
A A B
A A C
A B A
A B B
A B C
A C A
A C B
A C C
B A A
.....
and my problem is, I don't know, how to generate all combinations with unknown length. For example I want word length = 5 and program will generate all combination in exactly length 5. How to do it?
A A A A A
A A A A B
A A A A C
A A A B A
.........
(Sorry for my english)

Answer 1

See the link Print all permutations with repetition of characters
The below recursive function in the page, can create last+1 length permutations.
/* The main function that recursively prints all repeated
permutations of the given string. It uses data[] to store all
permutations one by one */
void allLexicographicRecur (char *str, char* data, int last, int index)
{
int i, len = strlen(str);
// One by one fix all characters at the given index and recur for
// the/ subsequent indexes
for ( i=0; i<len; i++ )
{
// Fix the ith character at index and if this is not the last
// index then recursively call for higher indexes
data[index] = str[i] ;
// If this is the last index then print the string stored in
// data[]
if (index == last)
printf("%s\n", data);
else // Recur for higher indexes
allLexicographicRecur (str, data, last, index+1);
}
}
I think this can serve your purpose.
Call allLexicographicRecur with the required (length-1) value for the 'last' parameter.

Answer 2

This is actually nothing more than counting.
If you have the letters A, B, and C, you are counting in base 3.
A is 0, B is 1 and C is 2.
Quick and dirty:
#include <string>
#include <iostream>
int main()
{
for(int i = 0; i < 100; i++) {
const int base = 3;
const char zero_char = 'A';
const size_t length = 5;
std::string out;
for(int n = i; n > 0; ) {
int d = n%base;
out = static_cast<char>(zero_char + d) + out;
n /= base;
}
while(out.length() < length) out = zero_char + out;
std::cout << out << '\n';
}
}
see it live
The possible combinations are baselength, so if you want all combinations for A, B, C with 5 digits, change the limit of the first for loop to 35 ( = 243):
for(int i = 0; i < 243; i++)

Answer 3

You may use something like:
bool increase(const std::string& s, std::vector<std::size_t>& it)
{
for (std::size_t i = 0, size = it.size(); i != size; ++i) {
const std::size_t index = size - 1 - i;
++it[index];
if (it[index] >= s.size()) {
it[index] = 0;
} else {
return true;
}
}
return false;
}
void do_job(const std::string& s,
const std::vector<std::size_t>& it)
{
for (std::size_t i = 0; i != it.size(); ++i) {
std::cout << s[it[i]] << " ";
}
std::cout << std::endl;
}
void cartesian_product(const std::string& s, std::size_t n)
{
std::vector<std::size_t> it(n, 0u);
do {
do_job(s, it);
} while (increase(s, it));
}
Demo