AlgoDaily - Build a Calculator

Build a Calculator (Hard)

Good afternoon! Here's our prompt for today.

You may see this problem at Microsoft, Google, Salesforce, Dropbox, Tableau Software, Yelp, Uber, Visa, Walmart Labs, Rubrik, Asana, Blend, Riot Games, and Proofpoint.

Let's build a very basic calculator by programming it! You've probably seen one that look similar to this:

But we won't be building a physical calculator (HardwareDaily will need to wait!)-- instead, we'll be writing a simple program that can serve as one. Can you write a function that will evaluate a simple expression string without using your language's eval method?

1expr = "2 + 2"
2calculator(expr)
3# 4

It should also be able to handle positive and negative symbols +,-, parentheses (), and spaces.

1expr = "3 - 1 + 2"
2calculator(expr)
3# 4
4
5expr = "(2+(4+2)-1)-(5+8)"
6calculator(expr)
7# -6

Assume for now that you don't need to handle multiplication or division cases.

Constraints

Length of the given string <= 100000
The numbers present in the string will be a single digit number
Expected time complexity : O(n)
Expected space complexity : O(n)

xxxxxxxxxx
 
def calculator(s):
    result = 0
    #
    return result
​
​
import unittest
​
​
class Test(unittest.TestCase):
    def test_1(self):
        assert calculator("2 + 2") == 4
        print("PASSED: assert calculator('2 + 2') == 4")
​
    def test_2(self):
        assert calculator("(2+2) - 3") == 1
        print("PASSED: assert calculator('(2+2) - 3') == 1")
​
    def test_3(self):
        assert calculator("-2-(-2)+(-5)") == -5
        print("PASSED: Negatives")
​
​
if __name__ == "__main__":
    unittest.main(verbosity=2)
    print("Nice job, 3/3 tests passed!")
​

OUTPUT

Results will appear here.