Permutations

1. Title

Permutations

2.   Http address

https://leetcode.com/problems/permutations/

3. The question

Given a collection of 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], and [3,2,1].

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4. My code (AC)

   public List<List<Integer>> permute(int[] nums) {
        
            List<List<Integer>> re = null;
            List<List<Integer>> bf = new ArrayList<List<Integer>>();
            Iterator<List<Integer>> it = null;
            List<Integer> list =null;
            List<Integer> addList =null;

            if( nums == null || nums.length <= 0 )
                    return bf;

            list = new ArrayList<Integer>();    
            list.add(nums[0]);
            bf.add(list);
            re = bf;
            for(int i = 1; i < nums.length; i++)
            {

                it = bf.iterator();
                re = new ArrayList<List<Integer>>();
                while(it.hasNext())
                {
                    list = it.next();
                    for(int j = 0 ; j <= list.size(); j++ )
                    {
                        addList = new ArrayList<Integer>(list);
                        addList.add(j,nums[i]);
                        re.add(addList);
                    }
                }
                bf = re;
            }
            return re;
    
    }