Sort Characters By Frequency.py

# Given a string, sort it in decreasing order based on the frequency of characters.

# Example 1:

# Input:
# "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:
# "cccaaa"

# Output:
# "cccaaa"

# Explanation:
# Both 'c' and 'a' appear three times, so "aaaccc" is also a valid answer.
# Note that "cacaca" is incorrect, as the same characters must be together.
# Example 3:

# Input:
# "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.


class Solution:
    def frequencySort(self, s: str) -> str:
        
        def Counter(s):
            d = {}
            for c  in s:
                d[c] = d.get(c,0)+1
            return d
        
        d= Counter(s)
        d= sorted(d.items(), key=lambda x: x[1], reverse=True)
        ans = ""
        for char in d:
            ans += char[0]*char[1]
        return ans