表达式求值

逆波兰算法，后缀表达式。
100.00%通过率；32ms运行时间；6520KB占用内存

# 逆波兰法 https://www.cnblogs.com/lulipro/p/7450886.html
priority = {'+': 0, '-': 0, '*': 1}
#
# 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
# 返回表达式的值
# @param s string字符串 待计算的表达式
# @return int整型
#
class Solution:
    def solve(self, s):
        # 中缀表达式转为后缀表达式
        stack = []
        l = []
        tempnum = ''
        for i in s:
            if i <= '9' and i >= '0':
                tempnum += i
                continue
            else:
                if tempnum != '':
                    l.append(tempnum)
                    tempnum = ''
                if i == '(':
                    stack.append(i)
                elif i == ')':
                    temp = stack.pop()
                    while temp != '(':
                        l.append(temp)
                        temp = stack.pop()
                else:
                    if (not stack) or stack[-1] == '(' or (stack[-1] >= '0' and stack[-1] <= '9'):
                        stack.append(i)
                    else:
                        if priority[stack[-1]] < priority[i]:
                            stack.append(i)
                        else:
                            while stack and (stack[-1] in priority) and (priority[stack[-1]] >= priority[i]):
                                l.append(stack.pop())
                            stack.append(i)
        if tempnum != '':
            l.append(tempnum)
        while stack:
            l.append(stack.pop())
        print(l)
        # 逆波兰法求后缀表达式的值
        for i in l:
            if i <= '9' and i >= '0':
                stack.append(i)
            else:
                num1 = int(stack.pop())
                num2 = int(stack.pop())
                temp = None
                if i == '*':
                    temp = num2*num1
                elif i == '-':
                    temp = num2-num1
                elif i == '+':
                    temp = num2+num1
                if temp:
                    stack.append(temp)
        return int(stack.pop())