Permutations.java

// Runtime: 2 ms (Top 76.85%) | Memory: 44.7 MB (Top 48.41%)
class Solution {
    List<List<Integer>> res = new LinkedList<>();

    public List<List<Integer>> permute(int[] nums) {
        ArrayList<Integer> list = new ArrayList<>();
        boolean[] visited = new boolean[nums.length];

        backTrack(nums, list, visited);
        return res;
    }

    private void backTrack(int[] nums, ArrayList<Integer> list, boolean[] visited){
        if(list.size() == nums.length){
            res.add(new ArrayList(list));
            return;
        }
        for(int i = 0; i < nums.length; i++){
            if(!visited[i]){
                visited[i] = true;
                list.add(nums[i]);
                backTrack(nums, list, visited);
                visited[i] = false;
                list.remove(list.size() - 1);
            }
        }
    }
}