<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:
    void rec(int &n, int t, int i, vector<pair<int,int>>& cd, vector<vector<int>>& ans, vector<int>& v)
    {
        if(t<0) return;
        if(i>n-1)
        {
            if(t==0)    ans.push_back(v);
            return;
        }
        int val = cd[i].first;
        int cnt = cd[i].second;

        // not take
        rec(n , t, i+1, cd, ans, v);

        // take
        for(int j = 1; j<=cnt; j++)
        {
            for(int k = 0; k<j; k++)
                v.push_back(val);

            rec(n, t-(val*j), i+1, cd, ans, v);

            for(int k = 0; k<j; k++)
                v.pop_back();
        }
        
    }
    vector<vector<int>> combinationSum2(vector<int>& cnd, int t) {
        int n  = cnd.size();
        sort(cnd.begin(), cnd.end());
        vector<pair<int,int>> cd;
        cd.push_back({cnd[0],1});
        int k = 0;
        for(int i = 1 ;i<n; i++)
        {
            if(cnd[i]==cnd[i-1])
            {
                cd[k].second++;
            }else
            {
                cd.push_back({cnd[i],1});
                k++;
            }
        }
        k++;
        // for(auto it:cd) cout<<it.first<<","<<it.second<<" ";
        // cout<<endl;
        vector<vector<int>> ans;
        vector<int> v;
        rec(k, t, 0, cd, ans, v);
        return ans;
    }
};
16839