原文(https://blog.csdn.net/zhangla1220/article/details/39060421)
题目：
Evaluate the value of an arithmetic expression in Reverse Polish Notation
Valid operators are +,-,*,/ Each operand may be an integer or another expression
Some examples:
["2", "1", "+", "3", "*"] -> ((2 + 1) * 3) -> 9
["4", "13", "5", "/", "+"] -> (4 + (13 / 5)) -> 6
代码：
def caculate(oper, x, y):
if oper== '+' :
return x+y
if oper== '-' :
return x-y
if oper== '*' :
return x*y
if oper== '/' :
return x/y
def evalRPN(tokens):
if (len(tokens) == 0):
return 0;
tokens_s = []
result = 0
i = 0;
x = 0
y = 0
for i in range(0,len(tokens)):
element = tokens[i]
if ((element== "+") or (element== "-") or (element== "*") or (element== "/")):
y = tokens_s.pop()
x = tokens_s.pop()
tokens_s.append(int(caculate(element,int(x),int(y))))
else:
tokens_s.append(int(element))
return (int)(tokens_s.pop())
tokens = []#test
print(evalRPN(tokens))
tokens = ["2", "1", "+", "3", "*"]#test
print(evalRPN(tokens))
