[LintCode] Permutations

/**
     * @param nums: A list of integers.
     * @return: A list of permutations.
     */
    public ArrayList<ArrayList<Integer>> permute(ArrayList<Integer> nums) {
        // write your code here
        ArrayList<ArrayList<Integer>> res = new ArrayList<ArrayList<Integer>>();
        if(nums == null || nums.size() == 0)
            return res;
        boolean[] visited = new boolean[nums.size()];
        ArrayList<Integer> tmp = new ArrayList<Integer>();
        dfs(res,visited, tmp, nums);
        return res;
    }
    public void dfs(ArrayList<ArrayList<Integer>> res, boolean[] visited, ArrayList<Integer> tmp, ArrayList<Integer> nums) {
        if(tmp.size() == nums.size()){
            res.add(new ArrayList<Integer>(tmp));
            return;
        }
        for(int i = 0 ; i < nums.size(); i++) {
            if(!visited[i]){
                visited[i] = true;
                tmp.add(nums.get(i));
                dfs(res, visited,tmp,nums);
                visited[i] = false;
                tmp.remove(tmp.size()-1);
            }
        }
    }