sherlock-and-valid-string.py

def isValid(s: str) -> bool:
    counter = Counter(s)
    freqList = counter.most_common(None)
    freqDict = defaultdict(list)
    for freqTuple in freqList:
        freqDict[freqTuple[1]].append(freqTuple[0])
    fd = dict(freqDict)
    if len(fd.keys()) == 1:
        return "YES"
    if len(fd.keys()) == 2:
        [k1, k2] = sorted(fd.keys())
        if k2 - k1 == 1 and len(fd[k2]) == 1:
            return "YES"
        if k1 == 1 and len(fd[k1])==1:
            return "YES"
    return "NO"