46. 全排列 (leetcode)

题目：
给定一个 没有重复 数字的序列，返回其所有可能的全排列。

示例:

输入: [1,2,3]
输出:
[
[1,2,3],
[1,3,2],
[2,1,3],
[2,3,1],
[3,1,2],
[3,2,1]
]

来源：https://leetcode-cn.com/problems/permutations

打卡（还不太理解）

class Solution:
    def permute(self, nums: List[int]) -> List[List[int]]:
        size = len(nums)
        if size == 0:
            return []

        used = [False for _ in range(size)]
        res = []
        self.dfs(nums, size, 0, [], used, res)
        return res

    def dfs(self,nums, size, depth, path, used, res):
            if depth == size:
                res.append(path[:])
                return

            for i in range(size):
                if not used[i]:
                    used[i] = True
                    path.append(nums[i])
                    self.dfs(nums, size, depth + 1, path, used, res)
                    used[i] = False
                    path.pop()