生成字符串的排列列表时出现问题

def permute(s):
    if len(s) == 1:
        return [s]
    
    result = []
    for i in range(len(s)):
        char = s[i]
        remaining_chars = s[:i] + s[i+1:]
        for p in permute(remaining_chars):
            result.append(char + p)
    
    return result

# 示例
print(permute("abc"))

def permute_unique(s):
    def backtrack(start):
        if start == len(s):
            result.add(''.join(s))
            return
        for i in range(start, len(s)):
            s[start], s[i] = s[i], s[start]  # 交换
            backtrack(start + 1)
            s[start], s[i] = s[i], s[start]  # 恢复
    
    result = set()
    s = list(s)
    backtrack(0)
    return list(result)

# 示例
print(permute_unique("aab"))