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9316e7c014
* flake8 --max-line-length=88
* fixup! Format Python code with psf/black push
Co-authored-by: github-actions <${GITHUB_ACTOR}@users.noreply.github.com>
94 lines
2.8 KiB
Python
94 lines
2.8 KiB
Python
"""
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Output:
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Enter an Infix Equation = a + b ^c
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Symbol | Stack | Postfix
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----------------------------
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c | | c
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^ | ^ | c
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b | ^ | cb
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+ | + | cb^
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a | + | cb^a
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| | cb^a+
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a+b^c (Infix) -> +a^bc (Prefix)
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"""
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def infix_2_postfix(Infix):
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Stack = []
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Postfix = []
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priority = {
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"^": 3,
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"*": 2,
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"/": 2,
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"%": 2,
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"+": 1,
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"-": 1,
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} # Priority of each operator
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print_width = len(Infix) if (len(Infix) > 7) else 7
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# Print table header for output
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print(
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"Symbol".center(8),
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"Stack".center(print_width),
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"Postfix".center(print_width),
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sep=" | ",
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)
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print("-" * (print_width * 3 + 7))
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for x in Infix:
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if x.isalpha() or x.isdigit():
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Postfix.append(x) # if x is Alphabet / Digit, add it to Postfix
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elif x == "(":
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Stack.append(x) # if x is "(" push to Stack
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elif x == ")": # if x is ")" pop stack until "(" is encountered
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while Stack[-1] != "(":
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Postfix.append(Stack.pop()) # Pop stack & add the content to Postfix
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Stack.pop()
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else:
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if len(Stack) == 0:
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Stack.append(x) # If stack is empty, push x to stack
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else: # while priority of x is not > priority of element in the stack
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while len(Stack) > 0 and priority[x] <= priority[Stack[-1]]:
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Postfix.append(Stack.pop()) # pop stack & add to Postfix
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Stack.append(x) # push x to stack
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print(
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x.center(8),
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("".join(Stack)).ljust(print_width),
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("".join(Postfix)).ljust(print_width),
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sep=" | ",
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) # Output in tabular format
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while len(Stack) > 0: # while stack is not empty
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Postfix.append(Stack.pop()) # pop stack & add to Postfix
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print(
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" ".center(8),
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("".join(Stack)).ljust(print_width),
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("".join(Postfix)).ljust(print_width),
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sep=" | ",
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) # Output in tabular format
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return "".join(Postfix) # return Postfix as str
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def infix_2_prefix(Infix):
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Infix = list(Infix[::-1]) # reverse the infix equation
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for i in range(len(Infix)):
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if Infix[i] == "(":
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Infix[i] = ")" # change "(" to ")"
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elif Infix[i] == ")":
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Infix[i] = "(" # change ")" to "("
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return (infix_2_postfix("".join(Infix)))[
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::-1
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] # call infix_2_postfix on Infix, return reverse of Postfix
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if __name__ == "__main__":
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Infix = input("\nEnter an Infix Equation = ") # Input an Infix equation
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Infix = "".join(Infix.split()) # Remove spaces from the input
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print("\n\t", Infix, "(Infix) -> ", infix_2_prefix(Infix), "(Prefix)")
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