Question

Input: BDCAbaxz

OUTPUT: AaBbCDxz

My solution is straight forward and ugly:

1. Sort the input with quick sort, then we get “ABCDabxz”

2. Alloc a temp array with the same size as the original one, then take the appropriate element from two sub-array(ptr1–>A, ptr2—>a)

3. Copy the temp array back to the original one

Any faster algorithm on this problem?

Answer 1

Yes.

Define a comparator for qsort that gives you the ordering you want in the first place (so rather than using AB...YZab...yz as the sort order, have it enforce AaBb...YyZz).