LeetCode 46：Permutations

public static List<List<Integer>> ans=new ArrayList<List<Integer>>();
    public static List<List<Integer>> permute(int[] nums) {
        int l=nums.length;
        List<Integer> temp=new ArrayList<Integer>();
        if(l==0)
        return ans;
        if(l==1){
            temp.add(nums[0]);
            ans.add(temp);
            return ans;
        }
        
        Arrays.sort(nums);
        dfs(temp, nums, new boolean[nums.length]);
        return ans;
        
    }
    
    public static void dfs(List<Integer> temp,int[] num,boolean [] used){
        if(temp.size() == num.length){  
            ans.add(new ArrayList(temp));//add a copy  
            return;  
        }   
        for(int i = 0; i < num.length; i++){  
            //if(i > 0 && !used[i-1] && num[i] == num[i-1]) continue;// judge duplicate number  
            if(!used[i]){  
                temp.add(num[i]);  
                used[i] = true;  
                dfs(temp, num, used);  
                temp.remove(temp.size() - 1);  
                used[i] = false;  
            }  
    }
    }