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, 0, 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 + 1, result, results);
            
            result.pop_back();
        }
    }
};