mirror of
https://github.com/TheAlgorithms/Python.git
synced 2024-10-06 05:39:30 +00:00
cecf43d648
* Pyupgrade to Python 3.9
* updating DIRECTORY.md
Co-authored-by: github-actions <${GITHUB_ACTOR}@users.noreply.github.com>
53 lines
1.3 KiB
Python
53 lines
1.3 KiB
Python
"""
|
|
The Reverse Polish Nation also known as Polish postfix notation
|
|
or simply postfix notation.
|
|
https://en.wikipedia.org/wiki/Reverse_Polish_notation
|
|
Classic examples of simple stack implementations
|
|
Valid operators are +, -, *, /.
|
|
Each operand may be an integer or another expression.
|
|
"""
|
|
from __future__ import annotations
|
|
|
|
from typing import Any
|
|
|
|
|
|
def evaluate_postfix(postfix_notation: list) -> int:
|
|
"""
|
|
>>> evaluate_postfix(["2", "1", "+", "3", "*"])
|
|
9
|
|
>>> evaluate_postfix(["4", "13", "5", "/", "+"])
|
|
6
|
|
>>> evaluate_postfix([])
|
|
0
|
|
"""
|
|
if not postfix_notation:
|
|
return 0
|
|
|
|
operations = {"+", "-", "*", "/"}
|
|
stack: list[Any] = []
|
|
|
|
for token in postfix_notation:
|
|
if token in operations:
|
|
b, a = stack.pop(), stack.pop()
|
|
if token == "+":
|
|
stack.append(a + b)
|
|
elif token == "-":
|
|
stack.append(a - b)
|
|
elif token == "*":
|
|
stack.append(a * b)
|
|
else:
|
|
if a * b < 0 and a % b != 0:
|
|
stack.append(a // b + 1)
|
|
else:
|
|
stack.append(a // b)
|
|
else:
|
|
stack.append(int(token))
|
|
|
|
return stack.pop()
|
|
|
|
|
|
if __name__ == "__main__":
|
|
import doctest
|
|
|
|
doctest.testmod()
|