Recently I got stuck on a question. Any help will be appreciated. Question is -

You are given an old touch smartphone numbers having dial pad and calculator app. The goal is to type a number on dialpad. Calculator have 1-9 and +, -, * , /, = as operations. But as 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: lets 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.