Location: https://leetcode.com/problems/evaluate-reverse-polish-notation/description/
You are given an array of strings tokens that represents an arithmetic expression in a Reverse Polish Notation.
Evaluate the expression. Return an integer that represents the value of the expression.
Note that:
The valid operators are '+', '-', '*', and '/'. Each operand may be an integer or another expression. The division between two integers always truncates toward zero. There will not be any division by zero. The input represents a valid arithmetic expression in a reverse polish notation. The answer and all the intermediate calculations can be represented in a 32-bit integer.
- Input: tokens = ["2","1","+","3","*"]
- Output: 9
- Explanation: ((2 + 1) * 3) = 9
- Input: tokens = ["4","13","5","/","+"]
- Output: 6
- Explanation: (4 + (13 / 5)) = 6
- Input: tokens = ["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
class Solution(object):
def evalRPN(self, tokens):
"""
:type tokens: List[str]
:rtype: int
"""
st = []
for t in tokens:
if t not in ['+', '-', '*', '/']:
st.append(int(t))
else:
r, l = st.pop(), st.pop()
if t == "+":
st.append(l+r)
elif t == '-':
st.append(l-r)
elif t == '*':
st.append(l*r)
else:
st.append(int(float(l)/r))
return st.pop(0)