Subsets II

Q:

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],
  []
]

A:

每次将所有相同的元素作为一个小的集合与前面得出的结果进行组合。如果S[i]到S[j]均相同，则result[j] = result[i] + (每个result[i]后面均分别append （1到j-i+1）个S[i])

class Solution {
public:
    vector<vector<int> > subsetsWithDup(vector<int> &S) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        vector<vector<int> > results;
        results.push_back(vector<int>());
        int cur = 0;
        int head = 0;
        int len = S.size();
        sort(S.begin(), S.end());
        while (cur < len) {
            while (cur < len && S[cur] == S[head]) {
                cur++;
            }
            int org_size = results.size();
            for (int i = 1; i <= cur - head; ++i) {
                
                for (int j = 0; j < org_size; ++j) {
                    results.push_back(results[j]);
                    results.back().insert(results.back().end(), i, S[head]);
                }
            }
            head = cur;
        }
        return results;
    }
};