given n=2
given array [1,2,3,4,5,6,7,8,9,10]
your program should output [2,1,4,3,6,5,8,7,10,9]

given n=3
given array [1,2,3,4,5,6,7,8,9,10]
your program should output [3,2,1,6,5,4,9,8,7,10]

given n=4
given array [1,2,3,4,5,6,7,8,9,10]
your program should output [4,3,2,1,8,7,6,5,10,9]