[leetcode 90] Subsets II

原创于 2015-01-11 14:41:58 发布 · 231 阅读

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#leetcode #backtracking #dfs

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本文介绍了一种解决含重复元素集合的所有可能子集问题的算法。通过先排序再使用深度优先搜索(DFS)的方法，确保了子集内元素的非递减顺序且不包含重复的子集。该算法适用于计算机科学中的组合生成问题。

Given a collection of integers that might contain duplicates, 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 = [1,2,2], a solution is:

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

class Solution {
public:
    vector<vector<int> > subsetsWithDup(vector<int> &S) {
        sort(S.begin(), S.end());
        vector<vector<int> > res;
        vector<int> path;
        dfs(S, 0, path, res);
        return res;
    }
    
    void dfs(const vector<int> &s, int start, vector<int> &path, vector<vector<int> > &res) {
        if (start == s.size()) {
            res.push_back(path);
            return ;
        }
        int prev = s[start]+1;
        for (int i = start; i < s.size(); i++) {
            if (prev == s[i]) {
                continue;
            }
            prev = s[i];
            path.push_back(s[i]);
            dfs(s, i+1, path, res);
            path.pop_back();
        }
        res.push_back(path);
        return ;
    }
};