Sort Characters By Frequency
https://leetcode.com/problems/sort-characters-by-frequency/
class Solution:
def frequencySort(self, s: str) -> str:
c = Counter(s)
srted = {k : v for k, v in sorted(c.items(), key=lambda item: -1 * item[1])}
return "".join(list(k * c[k] for k in srted))