Given a string s, return a new string where characters are grouped and ordered by decreasing frequency. If two characters have the same frequency, any relative order between them is valid.
s = "tree"Output"eert"Why`e` appears twice, so it must come before characters that appear once.s = "cccaaa"Output"cccaaa"Why`c` and `a` both appear three times, so either grouped order is acceptable.`1 <= len(s) <= 5 * 10^5``s` may contain letters, digits, and symbolsEqual frequencies may appear in any order