permutation template

List<List<Integer>> ans;

public List<List<Integer>> permute(int[] nums) {
    Arrays.sort(nums);
    ans = new ArrayList<List<Integer>>();
    HashSet<Integer> visited = new HashSet<Integer>();
    List<Integer> path = new ArrayList<Integer>();
    dfs(nums, path, visited);
    return ans;
}

public void (int[] nums, List<Integer> path, HashSet<Integer> visited) {
    if (path.size() == nums.length) {
        ans.add(new ArrayList<Integer>(path));
        return;
    }
    for (int i = 0; i < nums.length; ++i) {
        if (visited.contains(nums[i]))
            continue;
        visited.add(nums[i]);
        path.add(nums[i]);
        dfs(nums, path, visited);
        path.remove(path.size() - 1);
        visited.remove(nums[i]);
    }
}