mirror of
https://github.com/prdlk/leetcode.git
synced 2026-09-16 23:16:26 +00:00
89 lines
2.1 KiB
Python
89 lines
2.1 KiB
Python
|
"""
|
||
|
|
150. Evaluate Reverse Polish Notation
|
||
|
|
Difficulty: Medium
|
||
|
|
https://leetcode.com/problems/evaluate-reverse-polish-notation/
|
||
|
|
|
||
|
|
──────────────────────────────────────────────────
|
||
|
|
|
||
|
|
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.
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
Example 1:
|
||
|
|
|
||
|
|
Input: tokens = ["2","1","+","3","*"]
|
||
|
|
Output: 9
|
||
|
|
Explanation: ((2 + 1) * 3) = 9
|
||
|
|
|
||
|
|
Example 2:
|
||
|
|
|
||
|
|
Input: tokens = ["4","13","5","/","+"]
|
||
|
|
Output: 6
|
||
|
|
Explanation: (4 + (13 / 5)) = 6
|
||
|
|
|
||
|
|
Example 3:
|
||
|
|
|
||
|
|
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
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
Constraints:
|
||
|
|
|
||
|
|
• 1 <= tokens.length <= 10^4
|
||
|
|
|
||
|
|
• tokens[i] is either an operator: "+", "-", "*", or "/", or an
|
||
|
|
integer in the range [-200, 200].
|
||
|
|
"""
|
||
|
|
|
||
|
|
|
||
|
|
class Solution:
|
||
|
|
def evalRPN(self, tokens: List[str]) -> int:
|
||
|
|
stack = []
|
||
|
|
operations = {
|
||
|
|
"+": lambda x, y: int(x + y),
|
||
|
|
"-": lambda x, y: int(x - y),
|
||
|
|
"*": lambda x, y: int(x * y),
|
||
|
|
"/": lambda x, y: int(x / y),
|
||
|
|
}
|
||
|
|
|
||
|
|
for c in tokens:
|
||
|
|
if c in operations:
|
||
|
|
y = stack.pop()
|
||
|
|
x = stack.pop()
|
||
|
|
calc_func = operations[c]
|
||
|
|
result = calc_func(x, y)
|
||
|
|
stack.append(result)
|
||
|
|
else:
|
||
|
|
stack.append(int(c))
|
||
|
|
|
||
|
|
return stack[0]
|