how to get all possible combination from a set of integers and print in ascending order?

Question

input:
1 2
output:
1
2
12
21

Answer 1

range of integers?
number of integers?
is 1+22 in front of 1+1+3?

Answer 2

Simple- take a cartesian product of the sets and then order them by the leading element of the ordered pairs.

Answer 3

Here you go: https://code.sololearn.com/cI9pn9700N56 (use comb_all(); )