Skip to content

Update evaluate_postfix_notations.py #8758

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Closed
wants to merge 16 commits into from
Closed

Update evaluate_postfix_notations.py #8758

Changes from 11 commits
Commits
Show all changes
16 commits
Select commit Hold shift + click to select a range
005f9c5
Update evaluate_postfix_notations.py
rohan472000 May 22, 2023
4eb8123
[pre-commit.ci] auto fixes from pre-commit.com hooks
pre-commit-ci[bot] May 22, 2023
7646a57
Update evaluate_postfix_notations.py
rohan472000 May 22, 2023
de04120
Update evaluate_postfix_notations.py
rohan472000 May 22, 2023
9a92b82
[pre-commit.ci] auto fixes from pre-commit.com hooks
pre-commit-ci[bot] May 22, 2023
ecd9e74
Update evaluate_postfix_notations.py
rohan472000 Jun 11, 2023
3559a55
Update evaluate_postfix_notations.py
rohan472000 Jun 11, 2023
7f6a692
Update data_structures/stacks/evaluate_postfix_notations.py
rohan472000 Jun 12, 2023
748eff5
Update data_structures/stacks/evaluate_postfix_notations.py
rohan472000 Jun 12, 2023
816120b
Update data_structures/stacks/evaluate_postfix_notations.py
rohan472000 Jun 12, 2023
9e6f36a
Update data_structures/stacks/evaluate_postfix_notations.py
rohan472000 Jun 12, 2023
2779cd0
Update evaluate_postfix_notations.py
rohan472000 Jun 12, 2023
2bbac37
Update evaluate_postfix_notations.py
rohan472000 Jun 12, 2023
c4f050e
Update data_structures/stacks/evaluate_postfix_notations.py
rohan472000 Jun 12, 2023
c3a7c67
Update data_structures/stacks/evaluate_postfix_notations.py
rohan472000 Jun 12, 2023
29b28ec
Update evaluate_postfix_notations.py
rohan472000 Jun 13, 2023
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
34 changes: 24 additions & 10 deletions data_structures/stacks/evaluate_postfix_notations.py
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -17,6 +17,10 @@ def evaluate_postfix(postfix_notation: list) -> int:
9
>>> evaluate_postfix(["4", "13", "5", "/", "+"])
6
>>> evaluate_postfix(["2", "+"])
2
>>> evaluate_postfix(["5", "-"])
-5
>>> evaluate_postfix([])
0
"""
Expand All @@ -28,18 +32,28 @@ def evaluate_postfix(postfix_notation: list) -> int:

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)
if len(stack) < 2:
operand = stack.pop()
if token == "-":
operand = -operand
else:
raise ValueError(f"Unrecognized {token = }")
stack.append(operand)
Copy link
Contributor

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Suggested change
if len(stack) < 2:
operand = stack.pop()
if token == "-":
operand = -operand
else:
raise ValueError(f"Unrecognized {token = }")
stack.append(operand)
if token == "-":
if len(stack) == 1:
operand = stack.pop()
stack.append(-operand)
elif len(stack) == 0:
raise ValueError(f"Negation operator with no operand")

Currently, if there's only 1 operand on the stack but the token is not -, then it just appends the operand back onto the stack. This effectively leaves the stack exactly as it already was, so you can skip that altogether.

Furthermore, checking len(stack) < 2 includes the case in which the stack is empty. This should raise an error since there's no operand to negate.

Copy link
Contributor Author

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

I'm not able to commit above change requested...!!

else:
b, a = stack.pop(), stack.pop()
if token == "+":
stack.append(a + b)
elif token == "-":
stack.append(a - b)
elif token == "*":
stack.append(a * b)
elif token == "/":
if b == 0:
raise ValueError("Invalid expression: division by zero")
stack.append(a // b)
else:
msg = f"Unrecognized {token = }"
raise ValueError(msg)
else:
stack.append(int(token))

Expand Down