227.基本计算器-ii.py

#
# @lc app=leetcode.cn id=227 lang=python3
#
# [227] 基本计算器 II
#

# @lc code=start
class Solution:
    def calculate(self, s: str) -> int:
        s = s.replace(" ","")
        n = len(s)
        stack = []
        preSign = '+'
        num = 0
        for i in range(n):
            if s[i].isdigit():
                num = num * 10 + ord(s[i]) - ord('0')
            if i == n - 1 or s[i] in '+-*/':
                if preSign == '+':
                    stack.append(num)
                elif preSign == '-':
                    stack.append(-num)
                elif preSign == '*':
                    stack.append(stack.pop() * num)
                else:
                    stack.append(int(stack.pop() / num))
                preSign = s[i]
                num = 0
        return sum(stack)
        # return eval(s.replace('/','//'))
# @lc code=end

S = Solution()
print(S.calculate(" 3/2 "))