CompetitiveProgrammingSolutions/Basic Calculator II at main · Danitilahun/CompetitiveProgrammingSolutions · GitHub

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class Solution:
    def calculate(self, s: str) -> int:

        stack = []
        op = {"+","-","*", "/"}
        sign = "+"
        s= s.replace(" " , "")
        ind = 0

        while ind < len(s):
            num = ""
            while ind < len(s) and  s[ind] not in op:
                num += s[ind]
                ind += 1
            if sign == "+":
                stack.append(int(num))
            elif sign == "-":
                stack.append(-int(num))
            elif sign == "*":
                ans = stack.pop()
                stack.append(ans*int(num))
            elif sign == "/":
                ans = stack.pop()
                stack.append(int(ans / int(num)))
            if ind < len(s) : sign = s[ind]
            ind += 1

        return sum(stack)