BacktrackingString
On a phone keypad each digit maps to letters: 2=abc, 3=def, 4=ghi, 5=jkl, 6=mno, 7=pqrs, 8=tuv, 9=wxyz. Given a string of digits from 2 to 9, print every letter combination it could represent, one per line, in lexicographic order.
Input
A single line of digits from 2 to 9.
Output
One combination per line, in lexicographic order.
Constraints
1 <= length <= 6
Example 1
Input
23
Output
ad ae af bd be bf cd ce cf
ad ae af bd be bf cd ce cf, each on its own line.