Mastering the Art of Programming in Python 3/

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Solution Review: Prefix to Postfix Conversion

Solution Review: Prefix to Postfix Conversion

The solution to the 'Prefix to Postfix Conversion' challenge.

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Algorithm

Before moving onto the code, let’s see the following steps to solve the problem:

  • Scan the expression from right to left. For every symbol, check whether it’s an operator or operand.
    • If it is an operand, push it into the stack.
    • If it is an operator, pop from the stack two times.
      • Concatenate the popped items and the operator.
      • Push the concatenated result into the stack.
  • When traversing through the expression is complete, the stack will hold one element only, i.e., the final result (the postfix expression).
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from collections import deque
def postfix(prefix):
    stack = deque()
    prefix = ''.join((reversed(prefix)))    #Reversing the expression
    for symbol in prefix:
        if symbol != '+' and symbol != '-' and symbol != '*' and symbol != '/':
            stack.append(symbol)    # Push if an operand
        else:
            # If an operator, then pop two operands from stack
            operand1 = stack.pop()
            operand2 = stack.pop()
            # Concatenate operands and operator and again push it in stack
            stack.append(operand1+operand2+symbol)
            
    return(stack.pop()) # Poping the result
print(postfix('*-A/BC+/AKL'))
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