Permutations

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

For example, [1,2,3] have the following permutations:

[
  [1,2,3],
  [1,3,2],
  [2,1,3],
  [2,3,1],
  [3,1,2],
  [3,2,1]
]

Solution:

public class Solution {
    public List<List<Integer>> permute(int[] nums) {
        List<List<Integer>> ans = new ArrayList<>();
        ans.add(new ArrayList<Integer>());
        for(int i=0; i<nums.length; i++){
            List<List<Integer>> newAns = new ArrayList<>();
            for(List<Integer> list : ans){
                /* for every postion */
                for(int pos=0; pos<=i; pos++){
                    /* copy list */
                    List<Integer> newList = new ArrayList<>(list);
                    newList.add(pos, nums[i]);
                    newAns.add(newList);
                }
            }
            ans = newAns;
        }
        return ans;
    }
}