In-place merge of two arrays

Question

We have an array of size m+n in which m elements are present, in sorted order, and a second array of size n, again in sorted order. We want both of

Answer 1

Do a regular merge sort but in reverse comparing the largest numbers first, storing (reversed) into the end of the first array going backwards. This way, the elements you're merging are never overwritten (that this works is easy to see if you think about it for a moment).