451. Sort Characters By Frequency

Medium

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.

解題

func frequencySort(s string) string {
    count := make(map[byte]int)
    bytes := []byte(s)

    for _, c := range bytes {
        count[c]++
    }

    sort.Slice(bytes, func(i, j int) bool {
        if count[bytes[i]] == count[bytes[j]] {
            return bytes[i] > bytes[j]
        }
        return  count[bytes[i]] > count[bytes[j]]
    })

    return string(bytes)
}