[Python]中綴運算式轉首碼運算式

標籤：python   首碼運算式-尾碼表達   

#判斷運算子的優先順序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)

輸出

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

[Python]中綴運算式轉首碼運算式