46. 全排列

List<List<Integer>> res = new ArrayList<>();

    public List<List<Integer>> permute(int[] nums) {
        if (nums.length == 0)
            return res;
        int length = nums.length;
        List<Integer> temp = new ArrayList<>();
        for (int i = 0; i < nums.length; i++) {
            temp.add(nums[i]);
        }
        pereur(nums, temp, 0, length);
        return res;

    }

    private void pereur(int[] nums, List<Integer> lst, int level, int length) {
        if (level == length) {
            res.add(new ArrayList<Integer>(lst));
            System.out.println(lst);
            return;
        }

        for (int i = level; i < nums.length; i++) {
            Collections.swap(lst, level, i);
            pereur(nums, lst, level + 1, length);
            Collections.swap(lst, level, i);
        }

    }