High Stack Question 155 of 224

How do you evaluate an arithmetic expression string with +, -, parentheses, and spaces?

DSA interview set · Speak this in 60–90 seconds · Faridabad & Delhi NCR

StackLIFOlast in, first out

QueueFIFOfirst in, first out

Scan digits into a number, apply + or - on the running sign, and on '(' push (result, sign) then reset

Why interviewers care about Stack:

This is a process

question about Stack.

Panels listen for order,

trade-offs, and what you would actually do on a DSA project - not buzzwords.

Stay structured

Name the idea, why it exists, then one short example.

Close cleanly

End with when you use it and one common pitfall.

Before you speak the answer, walk the interviewer through these steps:

1
Scan digits into a
number, apply + or - on the running sign, and on '(' push (result, sign) then reset
2
Why it exists
on ')' pop and combine.
3
Time is O(n) and
space is O(n) for nesting depth.
4
A recursive descent parse
is equivalent and also O(n).
5
Common mistake
What juniors usually get wrong.
6
Close
When you pick this over the alternative.

Here's a short line you can speak, broken into clear beats:

Say this line

“Time is O(n) and space is O(n) for nesting depth.”

Break into beats

TimeisOnandspace

Speaking order

2987408337471632900

Note: Adapt this scaffold to your own project — keep it under 60–90 seconds.

Scan digits into a number, apply + or - on the running sign, and on '(' push (result, sign) then reset on ')' pop and combine.