def permutations(a):
    result = []
    helper(a, result, 0, len(a))
    return result


def helper(a, result, lo, hi):
    if lo == hi:
        print(a)
        result.append(a)
    else:
        cursor = lo
        for i in range(lo, hi):
            a[cursor], a[i] = a[i], a[cursor]
            helper(a, result, lo + 1, hi)
            a[cursor], a[i] = a[i], a[cursor]


if __name__ == '__main__':
    a = [1, 2, 3]
    re = permutations(a)
    print(re)

輸出：

實(shí)在想不通，為什么result中的值全是[1,2,3]