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.
Examples
Input:s = 'tree'
Output:'eert'
'e' appears twice while 'r' and 't' both appear once.
Constraints
• 1 <= s.length <= 5 * 10^5
• s consists of uppercase and lowercase English letters and digits.