For every element, we can define what is called a rank which is defined as the number of elements less than the particular element.

Now one thing to note that given two sorted arrays A and B to be merged into C, we can say Rank of an element in A + Rank of that element in B = Rank of that element in C. This is a very important concept we will be using.

Suppose A= [8,10,12,24] and B=[15,17,27,32]. .

In the above diagram one can see, if n processors are working in parallel, then rank of an element in A can be found in 0(1) time and rank of an element in B can be found out in 0(logn) time. Now we can add these ranks to find the index of the element in the merged array.