mirror of
https://github.com/TheAlgorithms/Python.git
synced 2024-11-27 23:11:09 +00:00
7d84f7fe61
* Create evaluate_postfix_notations.py Adding in the evaluate postfix notation using Stacks one of the common use with simple stack question creating a new file for the data structure of stacks * Create evaluate_postfix_notations.py Adding in the evaluate postfix notation using Stacks one of the common use with simple stack question creating a new file for the data structure of stacks * Delete evaluate_postfix_notations.py * Evaluate postfix expression stack clean approach Sending in the PR again as the Previous request failed in pre commit * Update evaluate_postfix_notations.py * Update evaluate_postfix_notations.py Made changes as per the required for fixing the failing pre-commits. * Update evaluate_postfix_notations.py Made changes as suggested by @cclauss * Update evaluate_postfix_notations.py fixed pre-commit fails * Update evaluate_postfix_notations.py fixing pre-commit fails * Update evaluate_postfix_notations.py Deleted trailing white spaces causing pre-commits to fail * Update data_structures/stacks/evaluate_postfix_notations.py Co-authored-by: Christian Clauss <cclauss@me.com> * Update data_structures/stacks/evaluate_postfix_notations.py Co-authored-by: Christian Clauss <cclauss@me.com> Co-authored-by: Christian Clauss <cclauss@me.com>
50 lines
1.2 KiB
Python
50 lines
1.2 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.
|
|
"""
|
|
|
|
|
|
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 = []
|
|
|
|
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()
|