[Python] infix expression to prefix expression

[Python] infix expression to prefix expression

# Priority def opOrder (op1, op2): order_dic = {'*': 4, '$': 5, '/': 4, '+': 3, '-': 3} if op1 = '(' or op2 = '(': return False elif op2 = ')': return True else: if order_dic [op1] <order_dic [op2]: return False else: return Truedef infix2prefix (string): prefix = ''stack = [] string_tmp ='' for s in string [: :-1]: if s = '(': string_tmp + = ') 'elif s =') ': string_tmp + =' ('else: string_tmp + = s for s in String_tmp: if s. isalpha (): prefix = s + prefix else: while len (stack) and opOrder (stack [-1], s): op = stack. pop () prefix = op + prefix if len (stack) = 0 or s! = ')': Stack. append (s) else: stack. pop () if len (stack): prefix = ''. join (stack) + prefix return prefixif _ name _ = '_ main _': for string in ['a + B * C ', '(A + B) * C',' (A-(B + C) * D) $ (E + F) ']: print string, '=>', infix2prefix (string)

Output

>>> A+B*C ==> +A*BC(A+B)*C ==> *+ABC((A-(B+C))*D)$(E+F) ==> $*-A+BCD+EF