Leetcode-Permutations

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].

 

Solution:一开始想递归来算Ann = An-1 n-1   * n（也就是在An-1 n-1基础之上在每个序列的元素缝隙之间插入数字N）

             干脆循环来算，从A11到A22再到Ann也差不多

 public List<List<Integer>> permute(int[] num) {
            List<List<Integer>> list = new ArrayList<List<Integer>>();
               List<Integer> l = new ArrayList<Integer>();
               l.add(num[0]);
               list.add(l);
            for(int i=1;i<num.length;i++){
                int listNum = list.size();
                for(int j=0;j<listNum;j++){                    
                    int k = 0;
                    int listNodeNum  = list.get(j).size();
                    while(k< listNodeNum){
                        List<Integer> subList =  new ArrayList<Integer>(list.get(j));
                        subList.add(k,num[i]);
                        list.add(subList);
                        k++;
                    }
                    list.get(j).add(k,num[i]);                    
                }
            }           
            return list;
        }