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Commit 88b6caa

Browse files
ashwekpoyea
authored andcommitted
fixed balanced_parentheses, Added infix-prefix & postfix evaluation (TheAlgorithms#621)
* Create infix_to_prefix_conversion.py * Create postfix_evaluation.py * Update balanced_parentheses.py
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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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"""
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Output:
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Enter a Postfix Equation (space separated) = 5 6 9 * +
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Symbol | Action | Stack
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-----------------------------------
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5 | push(5) | 5
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6 | push(6) | 5,6
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9 | push(9) | 5,6,9
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| pop(9) | 5,6
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| pop(6) | 5
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* | push(6*9) | 5,54
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| pop(54) | 5
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| pop(5) |
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+ | push(5+54) | 59
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Result = 59
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"""
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import operator as op
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def Solve(Postfix):
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Stack = []
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Div = lambda x, y: int(x/y) # integer division operation
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Opr = {'^':op.pow, '*':op.mul, '/':Div, '+':op.add, '-':op.sub} # operators & their respective operation
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# print table header
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print('Symbol'.center(8), 'Action'.center(12), 'Stack', sep = " | ")
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print('-'*(30+len(Postfix)))
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for x in Postfix:
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if( x.isdigit() ): # if x in digit
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Stack.append(x) # append x to stack
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print(x.rjust(8), ('push('+x+')').ljust(12), ','.join(Stack), sep = " | ") # output in tabular format
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else:
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B = Stack.pop() # pop stack
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print("".rjust(8), ('pop('+B+')').ljust(12), ','.join(Stack), sep = " | ") # output in tabular format
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A = Stack.pop() # pop stack
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print("".rjust(8), ('pop('+A+')').ljust(12), ','.join(Stack), sep = " | ") # output in tabular format
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Stack.append( str(Opr[x](int(A), int(B))) ) # evaluate the 2 values poped from stack & push result to stack
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print(x.rjust(8), ('push('+A+x+B+')').ljust(12), ','.join(Stack), sep = " | ") # output in tabular format
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return int(Stack[0])
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if __name__ == "__main__":
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Postfix = input("\n\nEnter a Postfix Equation (space separated) = ").split(' ')
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print("\n\tResult = ", Solve(Postfix))

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