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249. Divide and Conquer  Rearrange array elements in special order
Objective: Given an array of integers of size 2n, write an algorithm to arrange them such that first n elements and last n elements are set up in alternative manner. Say n = 3 and 2n elements are {x1, x2, x3, y1, y2, y3} , then result should be {x1, y1, x2, y2, x3, y3}
Example:
A [] = {1, 3, 5, 7, 9, 2, 4, 6, 8, 10}, n= 5 Output: {1, 2, 3, 4, 5, 6, 7, 8, 9, 10}
Approaches:
Brute Force:
One by one shift all the elements from the second half of the array to their correct positions in the left half of the array.
Time Complexity: O(n^2)
See the explanation below
Output:
1 2 3 4 5 6 7 8 9 10
Divide and Conquer:
 This solution will work only if the total number of elements is in 2i So total elements are either 2 or 4 or 8 or 16 ….and so on.
 Total length is 2n, take n elements around middle element.
 Swap n/2 elements on the left side from the middle element with n/2 elements on the right side from the middle element.
 Now divide the array into 2 parts, first n elements and last n elements.
 Repeat step 2, 3 on both the parts recursively.
Time Complexity: O(nlogn)
See the explanation below
Output:
[1, 2, 3, 4, 5, 6, 7, 8]