[LeetCode] Subsets

最新推荐文章于 2019-04-17 12:01:23 发布

原创最新推荐文章于 2019-04-17 12:01:23 发布 · 322 阅读

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本文介绍两种生成给定整数集合所有可能子集的方法。方法一使用位操作遍历所有组合，确保子集按非递减顺序排列且无重复。方法二采用递归方式生成子集，通过深度优先搜索构建解空间。

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],
  []
]

Solution 1:

class Solution {
public:
    vector<vector<int> > subsets(vector<int> &S) {
        sort(S.begin(), S.end());
        int len = S.size();
        vector<vector<int>> result;
        int maxNum = pow(2, len);
        for(int i = 0; i < maxNum; i++)
        {
            vector<int> temp;
            for(int j = 0; j < len; j++)
            {
                if(i & (1<<j))
                temp.push_back(S[j]);
            }
            result.push_back(temp);
        }
        return result;
    }
};

Solution 2:

class Solution {
public:
    vector<vector<int>> result;
    vector<vector<int> > subsets(vector<int> &S) {
        sort(S.begin(), S.end());
        result.clear();
        vector<int> temp;
        generate(S, temp, 0);
        return result;
    }
    void generate(vector<int> &S, vector<int> temp, int level)
    {
        if(level == S.size())
        {
            result.push_back(temp);
            return;
        }
        generate(S, temp, level+1);
        temp.push_back(S[level]);
        generate(S, temp, level+1);
    }
};