description is clear enough :)

You showed how to do it, why even bother about the description ? Description is fine.

me too :'(

hahahahahahahaha

Some reply about one part of your comment:

The phrase "maximum element" seems really misleading. Does that mean the element in the array with the biggest index, or the element in the array with the biggest value (regardless of its index)?

maximum element. Hmmmm... Generally speaking, that is the maximum value/number in the array. For [1,200,3], it should be 200. For [4,500,6], it should be 500. biggest index? Usually we call it by the last element.

The biggest element (value-wise) is 0... well, it doesn't matter how many itterations you make applying the second operation to the array, 0 - a[i] doesn't alter the original array at all.

0 - a[i] doesn't alter the original array? No, 0 - (-3) = 3, 0 - (+3) = -3 ;-)

A bad news to me. I'm not good at the English grammar ;-)
If I am allowed to use Chinese, I think I will write a rigorous and detailed description ;-)
69 guys passed the tests and submitted their solutions. It seems that my descrption is not SOOO bad, right?
I made the following changes:

1. changed A[i] to a[i]. Yes, A and a are the same ;-)
2. changed "find M - maximum element of the array......" 
   to 
   "find the maximum element value of the array;
    replace each element a[i] with (maximum element value - a[i])"
3. edit the examples, showing more details

Hope this will be helpful ;-)
Thank you for your feedback.