[LC] 150. Evaluate Reverse Polish Notation
2024-09-07 06:36:30
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
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
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