Leetcode 227. Basic Calculator II

https://leetcode.com/problems/basic-calculator-ii/

When there are '*' and '/', priority should be concerned.

Solution:

# T:O(n) S:O(n)
class Solution(object):
    def calculate(self, s):
        """
        :type s: str
        :rtype: int
        """
        operands, operators = [], []
        operand = ""
        for i in reversed(xrange(len(s))):
            if s[i].isdigit():
                operand += s[i]
                if i == 0  or not s[i-1].isdigit():
                    operands.append(int(operand[::-1]))
                    operand = ""
            elif s[i] == ')' or s[i] == '*' or s[i] == '/':
                operators.append(s[i])
            elif s[i] == '+' or s[i] == '-':
                while operators and \
                      (operators[-1] == '*' or operators[-1] == '/'):
                    self.compute(operands, operators)
                operators.append(s[i])
            elif s[i] == '(':
                while operators[-1] != ')':
                    self.compute(operands, operators)
                operators.pop()
                
        while operators:
            self.compute(operands, operators)
            
        return operands[-1]

    def compute(self, operands, operators):
        left, right = operands.pop(), operands.pop()
        op = operators.pop()
        if op == '+':
            operands.append(left + right)
        elif op == '-':
            operands.append(left - right)
        elif op == '*':
            operands.append(left * right)
        elif op == '/':
            operands.append(left / right)         

Run Time: 420 ms