Alternate Lower Upper String Sort

Given a string containing lowercase and uppercase letters. Sort it in such a manner that the uppercase and lowercase letters come in an alternate manner but in a sorted way.

Examples:

Input : bAwutndekWEdkd
Output :AbEdWddekkntuw
Explanation:
Here we can see that letter ‘A’, ’E’, ’W’ are sorted 
as well as letters “b, d, d, d, e, k, k, n, t, u, w” are sorted 
but both appears alternately in the string as far as possible.

Input :abbfDDhGFBvdFDGBNDasZVDFjkb
Output :BaBaDbDbDbDdDfFhFjFkGsGvNVZ

1) Count lower case characters in an array lCount[] 
2) Count upper case characters in another array uCount[] 
3) Modify strings using lCount[] and uCount[] 

Output: 

AbEdWddekkntuw

Time Complexity: O(n).

Auxiliary Space: O(max(n,26)), where n is the length of the string.

This is because when string is passed in the function it creates a copy of itself in stack.