思路：依然採用dfs+交換，多了去重步驟。

程式碼：

public class PermutationsII {

	public static void main(String[] args) {

		int[] num= {1,1,2};
		System.out.println(permute(num));
	}

	public static List<List<Integer>> permute(int[] nums) {
		List<List<Integer>> ls =new ArrayList<>();
		helpPermute(nums,0,ls);
		return ls;
	}

	private static void helpPermute(int[] nums, int index, List<List<Integer>> ls) {
		if(index>=nums.length)
		{
			List<Integer> list = new ArrayList<>();
			for (int i = 0; i < nums.length; i++) {
				list.add(nums[i]);
			}
			if(!ls.contains(list))
			ls.add(new ArrayList(list));
			return;
		}
		for (int i = index; i < nums.length; i++) {
			swap(nums,i,index);
			helpPermute(nums, index+1,ls);
			swap(nums,i,index);
			
		}
	}

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

 

輸出：