fix: Exercise10_FasterMerge.java

[XinXiaoIsMe]

I run your code and find it should be indexRight but not middle, this is a little mistake but confused me some time. I left a comment in issue#21 but later I think it's better to open a pull request. Thank you again for your contribution.

[reneargento]

I ran a few tests and using middle instead of indexRight seems to give correct results. Using indexRight also gives correct results, but we do extra comparisons that can be avoided.
I believe it is because when we reach the middle index in the loop, all elements between middle + 1 and indexRight are higher than the elements between low and middle (as they are sorted in a decreasing order). So they are already in the correct position in the main array and we can stop the loop.
If you find a counter case where using middle instead of indexRight gives an incorrect result let me know.

[XinXiaoIsMe]

I ran a few tests and using middle instead of indexRight seems to give correct results. Using indexRight also gives correct results, but we do extra comparisons that can be avoided. I believe it is because when we reach the middle index in the loop, all elements between middle + 1 and indexRight are higher than the elements between low and middle (as they are sorted in a decreasing order). So they are already in the correct position in the main array and we can stop the loop. If you find a counter case where using middle instead of indexRight gives an incorrect result let me know.

You are right! I am too careless. Thanks for your patience.

[yetanothercoder]

no sense to compare after leftIndex reaches the middle: this mean that up to this point of time - all items from sorted left half are less than sorted right half, so the merging is not needed anymore.