<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:
    vector<vector<int>> combinationSum2(vector<int>& candidates, int target) {
        sort(candidates.begin() , candidates.end());
        set<vector<int>>pairs;
        vector<int>currPair;
        constructPairs(candidates , target , 0 , 0 , currPair , pairs);
        vector<vector<int>>ret;
        for(auto itr = pairs.begin() ; itr != pairs.end() ; itr++){
            ret.push_back(*itr);
        }
        return ret;
    }
    void constructPairs(vector<int>&cand , int target , int idx , int sum , vector<int>currPair , set<vector<int>>&pairs){
        if(sum == target) pairs.insert(currPair);
        if(idx < cand.size() && sum + cand[idx] <= target){
            int i = idx , n = cand.size();
            while(i + 1 < n && cand[i + 1] == cand[i]) i++;
            int j = i + 1;
            while(i >= idx){
                constructPairs(cand , target , j , sum , currPair , pairs);
                if(sum + cand[idx] <= target){
                    sum += cand[idx];
                    currPair.push_back(cand[idx]);
                    if(i == idx) constructPairs(cand , target , j , sum , currPair , pairs);
                }
                else break;
                i--;
            }


            // constructPairs(cand , target , idx + 1 , sum , currPair , pairs);
            // currPair.push_back(cand[idx]);
            // constructPairs(cand , target , idx + 1 , sum + cand[idx] , currPair , pairs);
        }
        return;
    }
};
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