全排列II

【题目】给定一个可包含重复数字的序列，返回所有不重复的全排列。

示例:

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

public List<List<Integer>> permuteUnique(int[] nums) {
		List<List<Integer>> res = new ArrayList<List<Integer>>();
		List<Integer> list = new ArrayList<>();
		boolean[] flag = new boolean[nums.length];
		Arrays.sort(nums);
		huishuo(nums, list, res, flag);
		return res;
	}

	private void huishuo(int[] nums, List<Integer> list, List<List<Integer>> res, boolean[] flag) {
		if (list.size() == nums.length) {
			res.add(new ArrayList<>(list));
		}
		for (int i = 0; i < nums.length; i++) {
			if (flag[i]) {
				continue;
			}
			if (i > 0 && nums[i] == nums[i - 1] && !flag[i - 1])
				continue;
			flag[i] = true;
			list.add(nums[i]);
			huishuo(nums, list, res, flag);
			flag[i] = false;
			list.remove(list.size() - 1);
		}
	}