Question

我正在尝试创建将使用给定整数的代码，然后输出一组整数，所有这些都是输入整数的数字的旋转。

因此，如果我输入“ 197”，则输出应为“ 197”，“ 971”和“ 791”。

但是，当我尝试时：

def rotation(n):
  rotations = set()
  for i in range( len( str(n) ) ):
    n = int( str(n)[i:] + str(n)[:i] )
    rotations.add(n)

使用输入“ 197”，它仅返回“ 197”，“ 971”，而不返回“ 791”。

为什么会这样？

Answer 1

您快到了。除非您要在每次迭代中擦除输入n。使用另一个变量名。

def rotation(n):
  rotations = set()
  for i in range( len( str(n) ) ):
    m = int( str(n)[i:] + str(n)[:i] )
    rotations.add(m)
  return rotations

print(rotation(197))

我会使用集合理解来写成这样：

def rotation(number):
    str_number = str(number)
    return {
        int( str_number[i:] + str_number[:i] )
        for i in range(len(str_number))
    }

@Henry Woody的解决方案2也很好。而不是在每次迭代中将输入字符串旋转i，而是从上一次迭代中旋转1。

Answer 2

The way you have your code structured does duplicate rotation because you reassign n on each step of the loop and use the iteration variable i in your slices.

So the process in the loop from your example is:

i = 0
- You have n = 197 and the rotation logic does nothing with i = 0 so you add 197 to rotations
i = 1
- Again you have n = 197, and rotation logic makes n = 971 and you add that to rotations.
i = 2
- Now n = 971, and the rotation logic slices from index 2, but n has already been rotated so we have n = 197 again, which is added to rotations (and removed since rotations is a set). Basically n has already been rotated forward, and now it is being rotated forward 2 steps (back to the initial value and skipping over n = 719)

To fix this you can either:

1. Keep n at its initial value and on each step rotate n the full amount (i) and add that to rotation without modifying n. Like so:

def rotation(n):
  rotations = set()
  for i in range( len( str(n) ) ):
    rotations.add(int( str(n)[i:] + str(n)[:i] ))
  return rotations

2. Rotate n forward on each step, but only rotate it forward one position each time. Like so:

def rotation(n):
  rotations = set()
  for i in range( len( str(n) ) ):
    n = int( str(n)[1:] + str(n)[:1] )
    rotations.add(n)
  return rotations

Python-数字旋转

2 个答案: