Google Phone Screening, USA

Today I gave my google phone screening (phd early career). And I was not able to solve it in time. The problem was basically Basic calculator 1 with all the numbers converted to letters ( figured it out). I have to simplify the following expression which includes [letters, (,),+,-] Such as "a+b+(a-b)+((a-b)+2b)>>3a+2b"( order does not matter) I started with stack. but then realised it is little bit different than when there is number Could not came out all the if /else conditions properly. and time ran out. I have started taking preperations with leetcode for 3 months ( around 200 problems).But still I was not confident I would be able to clear google one. And I could not. It seems to me I am doing problems with patterns, but when some complicated problems come up I just can not solve it. Do i need to do more problems? I dont know!!

**The interviewer later told me the solution will have one dictionary to count the numbers of chars and dynamically update it. and one stack to process signs. **I beleive I saw this problem some where, may be leetcode discussion.