46 Permutations

 Given a collection of distinct integers, return all possible permutations.

Example:

Input: [1,2,3]
Output:
[
  [1,2,3],
  [1,3,2],
  [2,1,3],
  [2,3,1],
  [3,1,2],
  [3,2,1]
]
 
 
 public List<List<Integer>> permute(int[] nums) {
         List<List<Integer>> subset = new ArrayList();
         boolean[] used = new boolean[nums.length];
         dfs(subset,nums,new ArrayList(),used);
         return subset;
    }
    
     void dfs( List<List<Integer>> subset,int[] nums,List<Integer> current, boolean[] used){
                if(current.size()==nums.length){
                 subset.add(new ArrayList(current));
                    return;
                }
               
                for(int i=0;i<nums.length;i++){
                    if(used[i]==true)continue;
                    current.add(nums[i]);
                    used[i] = true;
                    dfs(subset,nums, current,used);
                    current.remove(current.size()-1);
                    used[i] = false;
                } 
    }