C++ (using recursion or stacks)

List stretch (string input, int k). A stretch of the input string is generated by repeating each character in order up to k times (and at least once). For input string "abc" and k = 2, the output list should have: abc, aabc, abbc, abcc, aabbc, aabcc, abbcc, aabbcc. (Again, the order does not matter.)