mathdatech/Python
1
0
Fork 0
mirror of https://github.com/TheAlgorithms/Python.git synced 2024-11-23 21:11:08 +00:00
Code Issues Packages Projects Releases Wiki Activity

fixes #8673; Add operator's associativity check for stacks/infix_to_p… (#8674)

Browse Source 
* fixes #8673; Add operator's associativity check for stacks/infix_to_postfix_conversion.py

* fix ruff N806 in stacks/infix_to_postfix_conversion.py

* Update data_structures/stacks/infix_to_postfix_conversion.py

Co-authored-by: Tianyi Zheng <tianyizheng02@gmail.com>

* Update data_structures/stacks/infix_to_postfix_conversion.py

Co-authored-by: Tianyi Zheng <tianyizheng02@gmail.com>

---------

Co-authored-by: Tianyi Zheng <tianyizheng02@gmail.com>
This commit is contained in:
AmirSoroush 2023-08-01 21:23:34 +03:00 committed by GitHub
parent c9a7234a95
commit ce218c57f1
No known key found for this signature in database
GPG Key ID: 4AEE18F83AFDEB23
1 changed files with 47 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

50
data_structures/stacks/infix_to_postfix_conversion.py
View File

@ -4,9 +4,26 @@ https://en.wikipedia.org/wiki/Reverse_Polish_notation
https://en.wikipedia.org/wiki/Shunting-yard_algorithm
"""
from typing import Literal
from .balanced_parentheses import balanced_parentheses
from .stack import Stack
PRECEDENCES: dict[str, int] = {
"+": 1,
"-": 1,
"*": 2,
"/": 2,
"^": 3,
}
ASSOCIATIVITIES: dict[str, Literal["LR", "RL"]] = {
"+": "LR",
"-": "LR",
"*": "LR",
"/": "LR",
"^": "RL",
}
def precedence(char: str) -> int:
"""
@ -14,7 +31,15 @@ def precedence(char: str) -> int:
order of operation.
https://en.wikipedia.org/wiki/Order_of_operations
"""
return {"+": 1, "-": 1, "*": 2, "/": 2, "^": 3}.get(char, -1)
return PRECEDENCES.get(char, -1)
def associativity(char: str) -> Literal["LR", "RL"]:
"""
Return the associativity of the operator `char`.
https://en.wikipedia.org/wiki/Operator_associativity
"""
return ASSOCIATIVITIES[char]
def infix_to_postfix(expression_str: str) -> str:
@ -35,6 +60,8 @@ def infix_to_postfix(expression_str: str) -> str:
'a b c * + d e * f + g * +'
>>> infix_to_postfix("x^y/(5*z)+2")
'x y ^ 5 z * / 2 +'
>>> infix_to_postfix("2^3^2")
'2 3 2 ^ ^'
"""
if not balanced_parentheses(expression_str):
raise ValueError("Mismatched parentheses")
@ -50,9 +77,26 @@ def infix_to_postfix(expression_str: str) -> str:
postfix.append(stack.pop())
stack.pop()
else:
while not stack.is_empty() and precedence(char) <= precedence(stack.peek()):
while True:
if stack.is_empty():
stack.push(char)
break
char_precedence = precedence(char)
tos_precedence = precedence(stack.peek())
if char_precedence > tos_precedence:
stack.push(char)
break
if char_precedence < tos_precedence:
postfix.append(stack.pop())
continue
# Precedences are equal
if associativity(char) == "RL":
stack.push(char)
break
postfix.append(stack.pop())
stack.push(char)
while not stack.is_empty():
postfix.append(stack.pop())
return " ".join(postfix)