Sort Characters by Frequency, Case, Alphabet

The function is given a string. Sort the characters and return a new string. Sorting conditions:

• Most frequent move in front.
• For the same frequency upper case characters move in front.
• For the same frequency and case sort them alphabetically.

Examples

frequency_sort("tree") ➞ "eert"

frequency_sort("cccaaa") ➞ "aaaccc"

frequency_sort("Aabb") ➞ "bbAa"

Notes

N/A