Challenge
Given a string s, sort it in decreasing order based on the frequency of the characters. The frequency of a character is the number of times it appears in the string.

Return the sorted string. If there are multiple answers, return any of them.

Example 1:

Input: s = "tree" Output: "eert" Explanation: 'e' appears twice while 'r' and 't' both appear once. So 'e' must appear before both 'r' and 't'. Therefore "eetr" is also a valid answer.

Example 2:

Input: s = "cccaaa" Output: "aaaccc" Explanation: Both 'c' and 'a' appear three times, so both "cccaaa" and "aaaccc" are valid answers. Note that "cacaca" is incorrect, as the same characters must be together.

Example 3:

Input: s = "Aabb" Output: "bbAa" Explanation: "bbaA" is also a valid answer, but "Aabb" is incorrect. Note that 'A' and 'a' are treated as two different characters.

Algorithm

• Find the frequencyof each character string.

To achieve this, the counter function, item method and bucket in python is used.

The Counter.items() method helps to see the elements of the list along with their respective frequencies in a tuple. 

Bucket Sort is a comparison-type algorithm which assigns elements of a list we want to sort in Buckets, or Bins. The contents of these buckets are then sorted, typically with another algorithm. After sorting, the contents of the buckets are appended, forming a sorted collection
Bucket Sort can be thought of as a scatter-order-gather approach towards sorting a list, due to the fact that the elements are first scattered in buckets, ordered within them, and finally gathered into a new, sorted list.

• sort in decreasing order

The string is now sorted in reverse order based on the frequency using the reverse function in python.