Golang: recursion - runtime 0 ms, Beats 100%
\n# Code\n\nfunc digitSum(s string, k int) string {\n    if len(s) <= k { return s }\n    result := split(s, k)\n    return digitSum(stringCount(result), k)\n}\
\n# Code\n```\nfunc digitSum(s string, k int) string {\n    if len(s) <= k { return s }\n    result := split(s, k)\n    return digitSum(stringCount(result), k)\n}\n\nfunc stringCount(strs []string) (result string) {\n    for _, elements := range strs {\n        sum := 0 \n        for _, item := range elements {\n            i, _ := strconv.Atoi(string(item))\n            sum += i\n        }\n        result += fmt.Sprint(sum)\n    }\n    return\n}\n\nfunc split(s string, k int) (result []string) {\n    if len(s) <= k { return []string{s} }\n    result = append(result, s[:k])\n    result = append(result, split(s[k:], k)...)\n    return\n}\n```
['Go']