05_BasicCalculator.py

# Question link - https://leetcode.com/problems/basic-calculator/description/?envType=study-plan-v2&envId=top-interview-150

class Solution:
    def calculate(self, s: str) -> int:
        # Initalize the curr and res 
        curr = res = 0

        # Define sign initially +ve as 1 
        sign = 1

        # Define stack for saving the state 
        stack = []

        for char in s:
            # If it is digit 
            if char.isdigit():
                # Process the digit but it can be 22 , 333
                curr = curr * 10 + int(char)
            elif char in ["+" , "-"]:
                res += sign * curr
                sign = 1 if char == "+" else -1
                curr = 0

            elif char == "(":
                stack.append(res)
                stack.append(sign)
                sign = 1
                res = 0

            elif char == ")":
                res += sign * curr
                res *= stack.pop()
                res += stack.pop()
                curr = 0

        # Just ignore the " " conditon for the else case
        # And if any char left , then calcuate te res = res + sign * curr 
        return res + sign * curr