2025-08-02 16:22:20 +0000 UTC

class Solution:
    def sortString(self, s: str) -> str:
        freqs = defaultdict(int)
        for char in s:
            freqs[char] += 1
        keys = list(freqs.keys())
        keys.sort(key = ord)
        length = len(keys)
        res = []
        while freqs:
            for i in itertools.chain(range(length), reversed(range(length))):
                key = keys[i]
                if key not in freqs:
                    continue
                res.append(key)
                freqs[key] -= 1
                if freqs[key] == 0:
                    freqs.pop(key)
        return "".join(res)