Question

这是一个非常愚蠢的问题，但我暂时没有使用它，也不记得怎么做了。我正在做一个递归问题，需要显示倒计时的数字，以基本显示递归是如何工作的。但是，我似乎无法弄明白。这是我的代码。

def main():

    #have user input first number
    x = int(input('Enter the first number: '))

    #have user input second number
    y = int(input('Enter the second number: '))

    #calculate result by calling recursive function
    result = mult(x, y)

    #print the result
    print(x, 'times', y, 'is', result)

#define a function that uses recursion
def mult(x, y):
    # create a loop to display the numbers
    count = y
    while count > 0:
        print('First number =', x, 'Second number =', count)
        count -= 1
    #use recursion to multiply the numbers
    if x == 0:
        return 0
    elif x == 1:
        return y
    else:
        return y + mult(x - 1, y)

main()

我需要输出来说明这一点：

Enter the first number: 5
Enter the second number: 7
First number = 5 Second Number = 7
First number = 5 Second Number = 6
First number = 5 Second Number = 5
First number = 5 Second Number = 4
First number = 5 Second Number = 3
First number = 5 Second Number = 2
First number = 5 Second Number = 1
5 times 7 = 35

所以它在大多数情况下都有效，但是现在它显示了这个：

Enter the first number: 5
Enter the second number: 7
First number = 5 Second number = 7
First number = 5 Second number = 6
First number = 5 Second number = 5
First number = 5 Second number = 4
First number = 5 Second number = 3
First number = 5 Second number = 2
First number = 5 Second number = 1
First number = 4 Second number = 7
First number = 4 Second number = 6
First number = 4 Second number = 5
First number = 4 Second number = 4
First number = 4 Second number = 3
First number = 4 Second number = 2
First number = 4 Second number = 1
First number = 3 Second number = 7
First number = 3 Second number = 6
First number = 3 Second number = 5
First number = 3 Second number = 4
First number = 3 Second number = 3
First number = 3 Second number = 2
First number = 3 Second number = 1
First number = 2 Second number = 7
First number = 2 Second number = 6
First number = 2 Second number = 5
First number = 2 Second number = 4
First number = 2 Second number = 3
First number = 2 Second number = 2
First number = 2 Second number = 1
First number = 1 Second number = 7
First number = 1 Second number = 6
First number = 1 Second number = 5
First number = 1 Second number = 4
First number = 1 Second number = 3
First number = 1 Second number = 2
First number = 1 Second number = 1
5 times 7 is 35

Answer 1

打印这两个数字的关键是跟踪递归。所以很自然地，数字必须从里面递归函数打印出来。换句话说，您不希望创建一个额外的循环（使用while）来显示数字，但递归是循环。

您还只想在每次递归步骤中打印一次数字。

可能另外让您感到困惑的是，您已在所需输出和递归的参数顺序之间交换了“first”/ x和“second”/ y的角色。（您希望输出中的“秒”数减少，但是减少x的第一个参数（mult）。）

它应该是这样的：

def mult(x, y): """Calculate x * y by using recursion.""" print('First number =', x, 'Second number =', y) if y == 0: return 0 elif y == 1: return x else: return x + mult(x, y - 1) if __name__ == '__main__': x = int(input('Enter the first number: ')) y = int(input('Enter the second number: ')) # calculate result by calling recursive function result = mult(x, y) # print the result print(x, 'times', y, 'is', result)

Answer 2

我认为您没有存储修改后的y值。因此，while循环应该如下所示：

y_temp = y
while y_temp > 0:
    print('First number =', x, 'Second number =', y_temp)
    y_temp -= 1

Answer 3

只需进行一项小改动，您需要更新y中while loop的值。

#create a loop to display the numbers
while y > 0:
    print('First number =', x, 'Second number =', y)
    y -= 1

Answer 4

您的while循环不在递归调用之内，因此y的值不会更新。将print语句移到mult函数内，位于if语句上方。

def mult(x, y):
    print('First number =', x, 'Second number =', y)
    print('First number =', x, 'Second number =', y - 1)
    if x == 0:
        return 0
    elif x == 1:
        return y
    else:
        return y + mult(x - 1, y)

Answer 5

您忘记更新y，但您没有减少y。

Python while循环减法

5 个答案: