<p>Given a collection of candidate numbers (<code>candidates</code>) and a target number (<code>target</code>), find all unique combinations in <code>candidates</code>&nbsp;where the candidate numbers sum to <code>target</code>.</p>

<p>Each number in <code>candidates</code>&nbsp;may only be used <strong>once</strong> in the combination.</p>

<p><strong>Note:</strong>&nbsp;The solution set must not contain duplicate combinations.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> candidates = [10,1,2,7,6,1,5], target = 8
<strong>Output:</strong> 
[
[1,1,6],
[1,2,5],
[1,7],
[2,6]
]
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> candidates = [2,5,2,1,2], target = 5
<strong>Output:</strong> 
[
[1,2,2],
[5]
]
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;=&nbsp;candidates.length &lt;= 100</code></li>
	<li><code>1 &lt;=&nbsp;candidates[i] &lt;= 50</code></li>
	<li><code>1 &lt;= target &lt;= 30</code></li>
</ul>

class Solution {
public:
    unordered_map<int, unordered_map<int, vector<vector<int>>>> UM;
    vector<vector<int>> R(vector<int>& O, vector<int>& F, int idx, int target) {
        if (idx < 0) {
            return vector<vector<int>>(target == 0);
        }
        if (UM[idx].find(target) != UM[idx].end()) return UM[idx][target];
        for (int j = 0; j <= F[idx] && j*O[idx] <= target; ++j) {
            vector<vector<int>> S = R(O, F, idx-1, target-j*O[idx]);
            for (auto& i: S) {
                for(int k = 0; k < j; ++k) i.push_back(O[idx]);
                UM[idx][target].emplace_back(move(i));
            }
        }
        return UM[idx][target];
    }
    vector<vector<int>> combinationSum2(vector<int>& candidates, int target) {
        sort(candidates.begin(), candidates.end());
        vector<int> O, F;
        for (int i = 0; i < candidates.size(); ++i) {
            if(! i || candidates[i] > candidates[i-1]) {
                O.push_back(candidates[i]); F.push_back(1);
            } else F.back()++;
        }
        UM.clear();
        return R(O, F, O.size()-1, target);
        
    }
};
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