题解 | #逆波兰表达式求值#

#
# 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
#
# 
# @param tokens string字符串一维数组 
# @return int整型
#
class Solution:
    def evalRPN(self , tokens: List[str]) -> int:
        # write code here
        stack = []
        for t in tokens:
            if t not in ["+", "-", "*", "/"]:
                stack.append(t)
            else:
                A = int(stack.pop())    # 先弹出的数字
                B = int(stack.pop())    # 后弹出的数字
                # 运算时，后弹出的数字在运算符前
                if t == "+":
                    stack.append(B + A)
                elif t == "-":
                    stack.append(B - A)
                elif t == "*":
                    stack.append(B * A)
                elif t == "/":
                    stack.append(B / A)
        return int(stack.pop())