Evaluate the value of an arithmetic expression in Reverse Polish Notation.
Valid operators are +, -, *, /. Each operand may be an integer or another expression.
Note:
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
class Solution: def evalRPN(self, tokens: List[str]) -> int: stack = [] import string nums = string.digits operator = [‘+‘, ‘-‘, ‘*‘, ‘/‘] for token in tokens: if token in operator: last_one = stack.pop() last_two = stack.pop() cur_val = self.helper(last_one, last_two, token) stack.append(cur_val) else: stack.append(int(token)) return stack.pop() def helper(self, last_one, last_two, operator): if operator == ‘+‘: return last_two + last_one elif operator == ‘-‘: return last_two - last_one elif operator == ‘*‘: return last_two * last_one elif operator == ‘/‘: # special case to get ceiling value if last_two * last_one < 0 and last_two % last_one != 0: return last_two // last_one + 1 else: return last_two // last_one else: return
[LC] 150. Evaluate Reverse Polish Notation
原文：https://www.cnblogs.com/xuanlu/p/11757292.html