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62 lines
2.8 KiB
Python
62 lines
2.8 KiB
Python
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"""
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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 = {'^':3, '*':2, '/':2, '%':2, '+':1, '-':1} # 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('Symbol'.center(8), 'Stack'.center(print_width), 'Postfix'.center(print_width), sep = " | ")
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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()): Postfix.append(x) # if x is Alphabet / Digit, add it to Postfix
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elif(x == '('): 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): Stack.append(x) #If stack is empty, push x to stack
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else:
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while( len(Stack) > 0 and priority[x] <= priority[Stack[-1]]): # while priority of x is not greater than priority of element in the stack
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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(x.center(8), (''.join(Stack)).ljust(print_width), (''.join(Postfix)).ljust(print_width), sep = " | ") # 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(' '.center(8), (''.join(Stack)).ljust(print_width), (''.join(Postfix)).ljust(print_width), sep = " | ") # 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] == '('): Infix[i] = ')' # change "(" to ")"
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elif(Infix[i] == ')'): Infix[i] = '(' # change ")" to "("
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return (infix_2_postfix("".join(Infix)))[::-1] # 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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