【问题】
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】
class Solution:
# @param tokens, a list of string
# @return an integer
def evalRPN(self, tokens):
stack = []
for item in tokens:
if item not in ("+", "-", "*", "/"):
stack.append(int(item))
else:
op2 = stack.pop()
op1 = stack.pop()
if item == "+":
stack.append(op1 + op2)
elif item == "-":
stack.append(op1 - op2)
elif item == "*":
stack.append(op1 * op2)
elif item == "/":
stack.append(int(op1 *1.0 / op2))
return stack[0]
