@arvin, @MiNiPanda
Now i got where you are going to be wrong...
let take your input 10,9,8,7,1,2,3,4 as per your approach
at low level ( consider it as ith level ) only one element---> no comparisons
( i - 1 )th level only 2 elements -----> 1 comparisons ( concentrate on 9, compared with 10 ) ===> after merging array look like 9,10 .... 7,8 .... 1,2... 3,4...
( i - 2 )th level only 4 elements -----> 2 comparisons ( concentrate on 9, compared with 7 and 8 ) ===> after merging array look like 7,8,9,10 .... 1,2,3,4... ====> note that in this case 9 should be change ( if an element compared with every element of the remaining divided array ( divided array should have atleast 2 numbers ) then most compared element of your array should change )
( i - 3 )th level only 4 elements -----> 0 comparisons ( concentrate on 9, compared with none ) ===> after merging array look like 1,2,3,4... 7,8,9,10.....