题目：

题解：

class Solution {
private:vector<pair<int, int>> freq;vector<vector<int>> ans;vector<int> sequence;public:void dfs(int pos, int rest) {if (rest == 0) {ans.push_back(sequence);return;}if (pos == freq.size() || rest < freq[pos].first) {return;}dfs(pos + 1, rest);int most = min(rest / freq[pos].first, freq[pos].second);for (int i = 1; i <= most; ++i) {sequence.push_back(freq[pos].first);dfs(pos + 1, rest - i * freq[pos].first);}for (int i = 1; i <= most; ++i) {sequence.pop_back();}}vector<vector<int>> combinationSum2(vector<int>& candidates, int target) {sort(candidates.begin(), candidates.end());for (int num: candidates) {if (freq.empty() || num != freq.back().first) {freq.emplace_back(num, 1);} else {++freq.back().second;}}dfs(0, target);return ans;}
};