[LeetCode]Subsets II-优快云博客

本文链接：https://blog.youkuaiyun.com/sunbaigui/article/details/8981319

本文介绍了一种用于生成包含重复元素集合的所有子集的算法。通过深度优先搜索(DFS)策略，确保子集不重复且元素按非递减顺序排列。采用两种实现方式：一种直接操作元素，另一种使用布尔标志数组来跟踪元素选择。

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class Solution {
//because Elements in a subset must be in non-descending order.
//so if we sort the vector first.
//If we choose an elem[i] into subset, then we should choose elem[j](i<j<n) into the subset,
//repeat this until there is no element left any more.
//But note: in the same level we can not choose multiple same elements as the new heads of the next subset. 

	void DFS(vector<int>& S, int curPos, vector<int>& oneSubset, vector<vector<int>>& allSubset)
	{
		allSubset.push_back(oneSubset);
		for (int i = curPos; i < S.size(); ++i)
		{
			if(i != curPos && S[i] == S[i-1]) continue;

			oneSubset.push_back(S[i]);
			DFS(S, i+1, oneSubset, allSubset);
			oneSubset.pop_back();
		}
		
	}
public:
	vector<vector<int> > subsetsWithDup(vector<int> &S) {
		// Start typing your C/C++ solution below
		// DO NOT write int main() function
		sort(S.begin(), S.end());
		vector<int> oneSubset;
		vector<vector<int>> allSubset;
		DFS(S, 0, oneSubset, allSubset);
		return allSubset;
	}
};

second time

class Solution {
public:
    void subsetUtil(vector<int>& S, vector<bool>& used, int curIdx, vector<int>& curPath, vector<vector<int> >& allPath)
    {
        if(curIdx == S.size())
        {
            allPath.push_back(curPath);
            return ;
        }
        
        subsetUtil(S, used, curIdx+1, curPath, allPath);
        if(curIdx >= 1 && S[curIdx] == S[curIdx-1] && used[curIdx-1] == false) return;
        used[curIdx] = true;
        curPath.push_back(S[curIdx]);
        subsetUtil(S, used, curIdx+1, curPath, allPath);
        curPath.pop_back();
        used[curIdx] = false;
    }
    vector<vector<int> > subsetsWithDup(vector<int> &S) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        sort(S.begin(), S.end());
        vector<bool> used(S.size(), false);
        vector<vector<int> > allPath;
        vector<int> curPath;
        subsetUtil(S, used, 0, curPath, allPath);
        return allPath;
    }
};