f698:後序運算式

Code

Correct Code

#data="6 3 / 1 4 - * 3 + 8 -"
def postfix(instr):
    list1=list(map(str,instr.split()))
    stack=[]
    #print("len=",len(list1))
    for i in range(len(list1)):
        if list1[i] not in "+-*/":
            stack.append(list1[i])
        else:
            a=stack.pop()
            b=stack.pop()
            ope=b+list1[i]+a
            #print("a=",a,"b=",b)
            #print("ope=",ope)
            stack.append(str(int(eval(ope))))
    #print(stack)
    return stack[0]
data=str(input())
ans=postfix(data)
print(ans)

不能用string直接算

如果用string直接算的話，長度和元素會算入空白!所以必須轉換成list，切出可用元素。
例如下面的code，data長度是5，而a會是空白

data="2 1 -"
print("data=",data)
#print("outer len",len(data))
def postfix (instr):
    stack=[]
    print("len=",len(instr))
    for i in range(len(instr)):
        if instr[i] not in "+-*/":
            stack.append(instr[i])
        else:
            a=stack.pop()
            b=stack.pop()
            ope=b+instr[i]+a
            print("a=",a,"b=",b)
            print("ope=",ope)
            stack.append(str(eval(ope)))
    print(stack)
    return stack[0]
ans=postfix(data)
print(ans)