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786b32431c
* add test to infix_to_postfix_conversion
* fixed pre-commit error
* fixed build error
* updating DIRECTORY.md
Co-authored-by: github-actions <${GITHUB_ACTOR}@users.noreply.github.com>
70 lines
2.0 KiB
Python
70 lines
2.0 KiB
Python
"""
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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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https://en.wikipedia.org/wiki/Shunting-yard_algorithm
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"""
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from .balanced_parentheses import balanced_parentheses
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from .stack import Stack
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def precedence(char: str) -> int:
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"""
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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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return {"+": 1, "-": 1, "*": 2, "/": 2, "^": 3}.get(char, -1)
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def infix_to_postfix(expression_str: str) -> str:
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"""
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>>> infix_to_postfix("(1*(2+3)+4))")
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Traceback (most recent call last):
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...
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ValueError: Mismatched parentheses
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>>> infix_to_postfix("")
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''
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>>> infix_to_postfix("3+2")
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'3 2 +'
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>>> infix_to_postfix("(3+4)*5-6")
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'3 4 + 5 * 6 -'
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>>> infix_to_postfix("(1+2)*3/4-5")
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'1 2 + 3 * 4 / 5 -'
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>>> infix_to_postfix("a+b*c+(d*e+f)*g")
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'a b c * + d e * f + g * +'
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>>> infix_to_postfix("x^y/(5*z)+2")
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'x y ^ 5 z * / 2 +'
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"""
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if not balanced_parentheses(expression_str):
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raise ValueError("Mismatched parentheses")
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stack = Stack()
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postfix = []
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for char in expression_str:
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if char.isalpha() or char.isdigit():
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postfix.append(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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stack.pop()
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else:
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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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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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from doctest import testmod
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testmod()
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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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