from Bio.SeqRecord import SeqRecord


def convert(dna):
    if isinstance(dna, SeqRecord):
        return str(dna.seq)
    return dna


def immediateNeighbors(dna):
    hood = set()
    add = hood.add
    mer = ['A', 'C', 'G', 'T']
    for i in range(0, len(dna)):
        for j in range(0, len(mer)):
            if dna[i] != mer[j]:
                add(dna[:i] + mer[j] + dna[i + 1:])
    return hood


def neighbors(dna, dist):
    dna = convert(dna)
    hood = [dna]
    extend = hood.extend
    for _ in range(0, dist):
        for j in range(0, len(hood)):
            extend(immediateNeighbors(hood[j]))
    return set(hood)


def mostFrequentKmers(dna, merSize, dist):
    dna = convert(dna)
    res = set()
    dict = {}
    get = dict.get
    freqMax = 0

    for i in range(0, len(dna) - merSize + 1):
        nbs = neighbors(dna[i:i + merSize], dist)
        for neighbor in nbs:
            f = get(neighbor, 0) + 1
            dict[neighbor] = f
            freqMax = max(f, freqMax)

    add = res.add
    for mer, freq in dict.items():
        if freq == freqMax:
            add(mer)
    return res