栈的应用

逆波兰表达式

stack=[]                       
s=input("请输入逆波兰表达式：")+" "
x=0
minus=False
for i in range(len(s)-1):
    ch=s[i]
    if ch>="0" and ch<="9": #处理2位数及以上
        x=x*10+int(ch)
    elif ch=="-" and s[i+1]!=" ":
        minus=True 
    elif ch==" ":
        if minus:
            stack.append(0-x)
        else:
            stack.append(x)
        print(stack)
        minus=False
        x=0
    else:
        if minus:
            x=0-x
        minus=False
        num1=stack.pop()
        num2=stack.pop()
        if ch=="+":
            x=num2+num1
        if ch=="-":
            x=num2-num1
        if ch=="*":
            x=num2*num1
        if ch=="÷":
            x=num2 / num1
print("后缀表达式计算结果为%d"%(x))