Given an array of integers, sort the array into a wave like array and return it,
In other words, arrange the elements into a sequence such that a1 >= a2 <= a3 >= a4 <= a5.....

Example:

Given [1, 2, 3, 4]

One possible answer : [2, 1, 4, 3]
Another possible answer : [4, 1, 3, 2]

NOTE : If there are multiple answers possible, return the one thats lexicographically smallest.
So, in example case, you will return [2, 1, 4, 3]

I know the O(nlogn) approach. Sort and swap in pair.