leetcode_1:permute

class Solution:
    def permute(self, nums: List[int]) -> List[List[int]]:
        res = []
        def helper(nums, temp):
            if not nums:
                if temp not in res:
                    res.append(temp)
            for i in range(len(nums)):
                helper(nums[:i] + nums[i + 1:], temp + [nums[i]])

        helper(nums, [])
        return res

class Solution:
    def permute(self, nums: List[int]) -> List[List[int]]:
        def helper(path):
            if len(path) == l:
                res.append(path[:])
            for i in range(l):
                if not used[i]:
                    used[i] = True
                    path.append(nums[i])
                    helper(path)
                    path.pop(-1)
                    used[i] = False

        l = len(nums)
        res = []
        used = [False for _ in nums]
        helper([])
        return res

class Solution {
public:
    void helper(vector<vector<int>>& res, vector<int>& output, int first, int len)
    {
        if (first == len)
        {
            res.emplace_back(output);
            return ;
        }
        for(int i = first; i < len; i++)
        {
            swap(output[first], output[i]);
            helper(res, output, first + 1, len);
            swap(output[first], output[i]);
        }

    }
    vector<vector<int>> permute(vector<int>& nums) {
        vector<vector<int>> res;
        helper(res, nums, 0, (int)nums.size());
        return res;
    }
};