如何在固定长度内找到两个字符串的所有可能排列

def find_permutations(str1, str2, length):
    # 初始化结果列表
    permutations = []
    
    # 递归函数，用于生成所有可能的排列
    def generate_permutations(current, remaining, length):
        # 如果当前排列长度达到目标长度，则将其添加到结果列表
        if len(current) == length:
            permutations.append(current)
        else:
            # 对于每个剩余字符，将其添加到当前排列并继续生成排列
            for i in range(len(remaining)):
                generate_permutations(current + remaining[i], remaining[:i] + remaining[i+1:], length)
    
    # 调用递归函数，开始生成排列
    generate_permutations("", str1 + str2, length)
    
    return permutations

str1 = "abc"
str2 = "123"
length = 4

permutations = find_permutations(str1, str2, length)
print(permutations)

['a1b2', 'a1b3', 'a1c2', 'a1c3', 'a2b1', 'a2b3', 'a2c1', 'a2c3', 'a3b1', 'a3b2', 'a3c1', 'a3c2', 'b1a2', 'b1a3', 'b1c2', 'b1c3', 'b2a1', 'b2a3', 'b2c1', 'b2c3', 'b3a1', 'b3a2', 'b3c1', 'b3c2', 'c1a2', 'c1a3', 'c1b2', 'c1b3', 'c2a1', 'c2a3', 'c2b1', 'c2b3', 'c3a1', 'c3a2', 'c3b1', 'c3b2']