Leetcode78. Subset

题目传送地址：https://leetcode.cn/problems/subsets/

运行效率：

代码如下 递归解法

class Solution {
    
   public List<List<Integer>> subsets(int[] nums) {
    
    List<List<Integer>> res = new ArrayList<>();
    int lastNum = nums[nums.length - 1]; //the last element of the current array
    //处理边界情况
    if(nums.length==1){
    
      List<Integer> list = new ArrayList<>();
      list.add(lastNum);
      res.add(Arrays.asList());
      res.add(list);
      return  res;
    }
    int[] subArray = Arrays.copyOf(nums, nums.length - 1);
    List<List<Integer>> subsets = subsets(subArray);
    res.addAll(subsets);  //A subset of the previous array is also part of the subset that belongs to the new array
    for (int i = 0; i < subsets.size(); i++) {
    
      List<Integer> list1 = new ArrayList<>(subsets.get(i));
      list1.add(lastNum);
      res.add(list1);
    }
    return res;
  }
}