如何基于给定字符集和层数生成多种组合序列，避免连续相同字符？

def generate_combinations(charset, layers, allow_repeats=False):
    results = []
    n = len(charset)
    all_ones = 0
    for _ in range(layers):
        all_ones = all_ones * n + 1
    for i in range(n**layers):
        if allow_repeats or i % all_ones != 0:
            combination = ""
            temp = i
            for _ in range(layers):
                combination = charset[temp % n] + combination
                temp //= n
            results.append(combination)
    return results

print(generate_combinations('ab', 2))  # ['ab', 'ba']
print(generate_combinations('ab', 2, True))  # ['aa', 'ab', 'ba', 'bb']
print(generate_combinations('ab', 3))  # ['aab', 'aba', 'abb', 'baa', 'bab', 'bba']
print(generate_combinations('abc', 2))  # ['ab', 'ac', 'ba', 'bc', 'ca', 'cb']

def generate_combinations_recursive(charset, layers, allow_repeats=False):
    results = []
    current_combination = [''] * layers

    def backtrack(index, previous_char):
        if index == layers:
            if not (not allow_repeats and previous_char):
                results.append("".join(current_combination))
            return
        for char in charset:
            current_combination[index] = char
            backtrack(index + 1, char == previous_char)

    for char in charset:
        current_combination[0] = char
        backtrack(1, False)

    return results

print(generate_combinations_recursive('AB', 2))  # ['AB', 'BA']
print(generate_combinations_recursive('AB', 2, True))  # ['AA', 'AB', 'BA', 'BB']
print(generate_combinations_recursive('AB', 3))  # ['AAB', 'ABA', 'ABB', 'BAA', 'BAB', 'BBA']
print(generate_combinations_recursive('ABC', 2))  # ['AB', 'AC', 'BA', 'BC', 'CA', 'CB']