Evaluate the value of an arithmetic expression in Reverse Polish Notation.
Valid operators are +, -, *, /. Each operand may be an integer or another expression.
Note:
Division between two integers should truncate toward zero.
The given RPN expression is always valid. That means the expression would always evaluate to a result and there won't be any divide by zero operation.
Example 1:
Input: ["2", "1", "+", "3", "*"]
Output: 9
Explanation: ((2 + 1) * 3) = 9
Example 2:
Input: ["4", "13", "5", "/", "+"]
Output: 6
Explanation: (4 + (13 / 5)) = 6
Example 3:
Input: ["10", "6", "9", "3", "+", "-11", "*", "/", "*", "17", "+", "5", "+"]
Output: 22
Explanation:
((10 * (6 / ((9 + 3) * -11))) + 17) + 5
= ((10 * (6 / (12 * -11))) + 17) + 5
= ((10 * (6 / -132)) + 17) + 5
= ((10 * 0) + 17) + 5
= (0 + 17) + 5
= 17 + 5
= 22
My code:
class Solution:
def evalRPN(self, tokens: List[str]) -> int:
if len(tokens)==0:
return None
result=[]
for item in tokens:
#print(result)
if item=="+":
tmp1=result[-1]
tmp2=result[-2]
result[-2]=int(tmp1)+int(tmp2)
result=result[:-1]
continue
if item=="-":
tmp1=result[-1]
tmp2=result[-2]
result[-2]=int(tmp2)-int(tmp1)
result=result[:-1]
continue
if item=="*":
tmp1=result[-1]
tmp2=result[-2]
result[-2]=int(tmp2)*int(tmp1)
result=result[:-1]
continue
if item=="/":
tmp1=result[-1]
tmp2=result[-2]
result[-2]=int(int(tmp2)/int(tmp1))
result=result[:-1]
continue
result.append(item)
assert len(result)==1
return int(result[0])
Solution: https://leetcode.com/problems/evaluate-reverse-polish-notation/