I found an interesting problem on https://www.codewars.com/kata/584cfac5bd160694640000ae:
You're given a string of dominos. For each slot, there are 3 options:

  * "|" represents a standing domino

  * "/" represents a knocked over domino

  * " " represents a space where there is no domino

For example: 

```python
"||| ||||//| |/"
```

What you must do is find the resulting string if the first domino is pushed over. Now, tipping a domino will cause the next domino to its right to fall over as well, but if a domino is already tipped over, or there is a domino missing, the reaction will stop.

So in out example above, the result would be:

"/// ||||//| |/"

since the reaction would stop as soon as it gets to a space.

I tried it in Python, but could not do it. Can you solve it?
def domino_reaction(s):
    i = next((i for i,j in enumerate(s) if j in "/ "),len(s))
    return "/"*i+s[i:]