全排列 II

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]
]

class Solution {
     public List<List<Integer>> permuteUnique(int[] nums) {
        List<List<Integer>> L = new ArrayList<>();
        perm2(nums, 0, L);
        return L;
        
    }

    public static void perm2(int[] nums, int start, List<List<Integer>> L) {
        if (start == nums.length) {
            List<Integer> list = new ArrayList<>();
            for (int n : nums) {
                list.add(n);
            }
            boolean f = true;
            if (L.size() != 0) {
                for (int i = 0; i < L.size(); ++i) {
                    if(L.get(i).equals(list)) {
                        f = false;

                        break;
                    }
                }
            }
            if (f) {
                L.add(list);
            }
            return;

        }

        for (int i = start; i < nums.length; i++) {
            swap(nums, start, i);
            perm2(nums, start + 1, L);

            swap(nums, i, start);
        }


    }
    
     public static void swap(int[] nums, int i, int j) {
        int temp = nums[i];
        nums[i] = nums[j];
        nums[j] = temp;
    }
}