mirror of
https://github.com/TheAlgorithms/Python.git
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4d0a8f2355
* optimized recursive_bubble_sort
* Fixed doctest error due whitespace
* reduce loop times for optimization
* fixup! Format Python code with psf/black push
Co-authored-by: github-actions <${GITHUB_ACTOR}@users.noreply.github.com>
60 lines
1.8 KiB
Python
60 lines
1.8 KiB
Python
import string
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from .stack import Stack
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__author__ = "Omkar Pathak"
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def is_operand(char):
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return char in string.ascii_letters or char in string.digits
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def precedence(char):
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"""Return integer value representing an operator's precedence, or
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order of operation.
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https://en.wikipedia.org/wiki/Order_of_operations
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"""
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dictionary = {"+": 1, "-": 1, "*": 2, "/": 2, "^": 3}
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return dictionary.get(char, -1)
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def infix_to_postfix(expression):
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"""Convert infix notation to postfix notation using the Shunting-yard
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algorithm.
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https://en.wikipedia.org/wiki/Shunting-yard_algorithm
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https://en.wikipedia.org/wiki/Infix_notation
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https://en.wikipedia.org/wiki/Reverse_Polish_notation
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"""
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stack = Stack(len(expression))
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postfix = []
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for char in expression:
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if is_operand(char):
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postfix.append(char)
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elif char not in {"(", ")"}:
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while not stack.is_empty() and precedence(char) <= precedence(stack.peek()):
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postfix.append(stack.pop())
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stack.push(char)
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elif char == "(":
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stack.push(char)
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elif char == ")":
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while not stack.is_empty() and stack.peek() != "(":
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postfix.append(stack.pop())
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# Pop '(' from stack. If there is no '(', there is a mismatched
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# parentheses.
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if stack.peek() != "(":
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raise ValueError("Mismatched parentheses")
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stack.pop()
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while not stack.is_empty():
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postfix.append(stack.pop())
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return " ".join(postfix)
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if __name__ == "__main__":
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expression = "a+b*(c^d-e)^(f+g*h)-i"
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print("Infix to Postfix Notation demonstration:\n")
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print("Infix notation: " + expression)
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print("Postfix notation: " + infix_to_postfix(expression))
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