如何用Python编写求解排列组合的算法？

def permute(nums):    res = []    backtrack(nums, [], res)    return resdef backtrack(nums, path, res):    if not nums:        res.append(path)    for i in range(len(nums)):        backtrack(nums[:i] + nums[i+1:], path + [nums[i]], res)

print(permute([1, 2, 3]))# 输出：# [[1, 2, 3], [1, 3, 2], [2, 1, 3], [2, 3, 1], [3, 1, 2], [3, 2, 1]]

def combine(n, k):    res = []    backtrack(n, k, [], res, 1)    return resdef backtrack(n, k, path, res, start):    if k == 0:        res.append(path)        return    for i in range(start, n + 1):        backtrack(n, k - 1, path + [i], res, i + 1)

print(combine(4, 2))# 输出：# [[1, 2], [1, 3], [1, 4], [2, 3], [2, 4], [3, 4]]