451. Sort Characters By Frequency

문제)

451. Sort Characters By Frequency

 

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.

 

Constraints:

• 1 <= s.length <= 5 * 105
• s consists of uppercase and lowercase English letters and digits.

 

솔루션1)

sorted()  함수 멀티 정렬 기능 사용하면 손 쉽게 해결 가능

class Solution:
    def frequencySort(self, s: str) -> str:
        # to dict with frequency
        c = Counter(s)        

        # to list
        char_freq = list(c.items())

        # sorting by frequency, character
        char_freq = sorted(char_freq, key=lambda x: (-x[1], x[0]))

        return ''.join([item[0] * item[1] for item in char_freq])