2014. Longest Subsequence Repeated k Times (hard)

s = "letsleetcode", k = 2

s에서 k번 반복하는 가장 긴 sub string을 찾아서 리턴

filtered = "".join(el*(freq//k) for el, freq in collections.Counter(s).items()) def dfs(n, sel, seq, res):     if len(seq) == n:         res.add(''.join(seq))         return     for i in range(len(filtered)):         if i in sel:             continue         dfs(n, sel + [i], seq + [filtered[i]], res) def is_subseq(sub, seq):     seq = iter(seq)     return all(c in seq for c in sub) combs = set() for i in range(1, len(filtered) + 1):     dfs(i, [], [], combs) combs = sorted(combs, key=lambda p: (len(p), p), reverse=True) for c in combs:     if is_subseq(c*k, s):         return c return ''