You are given an old touch smartphone numbers having dial pad and calculator app.

The goal is to type a number on dial-pad.

Calculator have 1-9 and +, -, * , /, = as operations. But as the phone is old, some of the numbers and some operations can’t be touched.

But you can always make a number using other numbers and operations. There could be multiple ways of making a number. You have to find minimum operation for making a number.

For ex: let’s say 1,4,6,7,8,9 works and +,-,* works.

2,3,5 and / doesn’t work.

If you have to type 18-> 2 operations. (Each touch is considered an operation).

If you have to type 5 -> ‘1+4=’ that requires 4 operations. There could be other ways to make ‘5’.

The goal is to find minimum operations.

Link to the question: https://www.careercup.com/question?id=5680648437104640

Please help me in understanding the approach. Thank you