题目：

题解：

func frequencySort(s string) string {
    cnt := map[byte]int{}
    maxFreq := 0
    for i := range s {
        cnt[s[i]]++
        maxFreq = max(maxFreq, cnt[s[i]])
    }

    buckets := make([][]byte, maxFreq+1)
    for ch, c := range cnt {
        buckets[c] = append(buckets[c], ch)
    }

    ans := make([]byte, 0, len(s))
    for i := maxFreq; i > 0; i-- {
        for _, ch := range buckets[i] {
            ans = append(ans, bytes.Repeat([]byte{ch}, i)...)
        }
    }
    return string(ans)
}

func max(a, b int) int {
    if a > b {
        return a
    }
    return b
}