subsets leetcode

Given a set of distinct integers, S, return all possible subsets.

Note:

• Elements in a subset must be in non-descending order.
• The solution set must not contain duplicate subsets.

For example,
If S = [1,2,3], a solution is:

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

  public class Solution {
    public ArrayList<ArrayList<Integer>> subsets(int[] S) {
        ArrayList<ArrayList<Integer>> result = new ArrayList<ArrayList<Integer>>();
        if(S.length== 0 || S== null){
            return result;
        }
        ArrayList<Integer> tem = new ArrayList<Integer>();
        Arrays.sort(S);
        dfs(result,tem,S,0);
        return result;
        
    }
    private void dfs(ArrayList<ArrayList<Integer>> result, ArrayList<Integer> tem,int[] S,int pos){
        result.add(new ArrayList<Integer>(tem));
        for(int i = pos; i < S.length; i++){
            tem.add(S[i]);
            dfs(result,tem,S,i+1);
            tem.remove(tem.size()-1);
        }
    } 
}

1 java中的length属性是针对数组说的,比如说你声明了一个数组,想知道这个数组的长度则用到了length这个属性.

2 java中的length()方法是针对字符串String说的,如果想看这个字符串的长度则用到length()这个方法.

3.java中的size()方法是针对泛型集合说的,如果想看这个泛型有多少个元素,就调用此方法来查看!

这个例子来演示这两个方法和一个属性的用法

 public static void main(String[] args) {
        String []list={"ma","cao","yuan"};
        String a="macaoyuan";
        System.out.println(list.length);
        System.out.println(a.length());
        List<Object> array=new ArrayList();
        array.add(a);
        System.out.println(array.size());
    }

输出的值为:

3

9

1