17. Subsets【medium】

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

Notice

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

Example

If S = [1,2,3], a solution is:

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

Challenge

Can you do it in both recursively and iteratively?

题意

给定一个含不同整数的集合，返回其所有的子集

注意事项

子集中的元素排列必须是非降序的，解集必须不包含重复的子集

解法一：

 class Solution {
 public:
     /*
      * @param nums: A set of numbers
      * @return: A list of lists
      */
     vector<vector<int>> subsets(vector<int> &nums) {
         // write your code here
         vector<vector<int> > results;
         vector<int> result;

         sort(nums.begin(), nums.end());

         helper(nums, , result, results);

         return results;
     }

     void helper(vector<int> &nums, int start, vector<int> & result, vector<vector<int> > & results)
     {
         results.push_back(result);

         for (int i = start; i < nums.size(); ++i) {
             result.push_back(nums[i]);

             helper(nums, i + , result, results);

             result.pop_back();
         }
     }
 };