Question

因此，对于我的任务，我应该编写一个带有2个无符号参数并输出其产品的函数。

unsigned multiply( unsigned a, unsigned b );

例如，

multiply(3, 4)

应该返回12

问题是，我不允许使用+， - ，/，*或％运算符。我只允许调用函数，并使用++和 - 。

递增/递减

我还有另外一个添加2个参数的函数：

unsigned add(unsigned a, unsigned b)
{
    if (a > 0)
        add(--a, ++b);
    else return(b);
}

我可以调用它，以及我需要的任何帮助函数。

我在过去的30分钟里尝试了各种排列，但我无法正确地计算数学;我最接近的是让自己加倍一次，但这不会削减它。有什么想法吗？

编辑：忘了提！ for / while循环不允许

Answer 1

unsigned add(unsigned a, unsigned b){
    if (a > 0)
        return add(--a, ++b);
    else
        return b;
}
unsigned multiply( unsigned a, unsigned b ){
    if( a > 0)
        return add(b, multiply(--a, b));
    else
        return 0;
}

Answer 2

{{1}}

当然，如果必须使用递归，这将无效。

Answer 3

我没有编译它，但我确定它的工作

Sub StandardEntry()
    If ActiveCell.Value = "Yes" And ActivCell.Offset(0, -1).Value = "Term 1" And ActiveCell.Offset(0, -2).Value = "CLV 7" Then
        CLV7Term1
    Else
    If ActiveCell.Value = "Yes" And ActiveCell.Offset(0, -1).Value = "Term 2" And ActiveCell.Offset(0, -2).Value = "CLV 7" Then
        CLV7Term2
    Else
    If ActiveCell.Value = "Yes" And ActiveCell.Offset(0, -1).Value = "Term 3" And ActiveCell.Offset(0, -2).Value = "CLV 7" Then
        CLV7Term3
    Else
    If ActiveCell.Value = "Yes" And ActiveCell.Offset(0, -1).Value = "Term 4" And ActiveCell.Offset(0, -2).Value = "CLV 7" Then
        CLV7Term4
    Else
    If ActiveCell.Value = "Yes" And ActiveCell.Offset(0, -1).Value = "Term 1" And ActiveCell.Offset(0, -2).Value = "CLV 8" Then
        CLV8Term1
    Else
    If ActiveCell.Value = "Yes" And ActiveCell.Offset(0, -1).Value = "Term 2" And ActiveCell.Offset(0, -2).Value = "CLV 8" Then
        CLV8Term2
    Else
    If ActiveCell.Value = "Yes" And ActiveCell.Offset(0, -1).Value = "Term 3" And ActiveCell.Offset(0, -2).Value = "CLV 8" Then
        CLV8Term3
    Else
    If ActiveCell.Value = "Yes" And ActiveCell.Offset(0, -1).Value = "Term 4" And ActiveCell.Offset(0, -2).Value = "CLV 8" Then
        CLV8Term4
    Else
    If ActiveCell.Value = "Yes" And ActiveCell.Offset(0, -1).Value = "Term 1" And ActiveCell.Offset(0, -2).Value = "CLV 9" Then
        CLV9Term1
    Else
    If ActiveCell.Value = "Yes" And ActiveCell.Offset(0, -1).Value = "Term 2" And ActiveCell.Offset(0, -2).Value = "CLV 9" Then
        CLV9Term2
    Else
    If ActiveCell.Value = "Yes" And ActiveCell.Offset(0, -1).Value = "Term 3" And ActiveCell.Offset(0, -2).Value = "CLV 9" Then
        CLV9Term3
    Else
    If ActiveCell.Value = "Yes" And ActiveCell.Offset(0, -1).Value = "Term 4" And ActiveCell.Offset(0, -2).Value = "CLV 9" Then
        CLV9Term4
    End If
    End If
    End If
    End If
    End If
    End If
    End If
    End If
    End If
    End If
    End If
    End If 
End Sub

Answer 4

这是一个尾递归解决方案，它使用辅助函数和累加器。这与使用嵌套for循环的解决方案基本相同：

unsigned multiply(unsigned a, unsigned b)
{
    return mult_helper(a, b, 0, a);
}

unsigned mult_helper(unsigned a, unsigned b, unsigned acc, unsigned reset)
{
    if (b == 0)
        return acc;
    if (a > 0)
        return mult_helper(--a, b, ++acc, reset);
    return mult_helper(reset, --b, acc, reset);
}

在C中仅使用递归函数和递增相乘

4 个答案: