<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 {
    vector<vector<int>> solve(vector<int>& candidates, int target, int idx) {
        if (target == 0) {
            return {{}};
        }
        if (idx < 0 || target < 0) {
            return {};
        }

        vector<vector<int>> res;
        
        int x = idx-1;
        while(x >= 0 && candidates[x] == candidates[idx]) {
            x--;
        }

        vector<int> v;
        
        for (int i = idx; i > x; i--) {
            v.push_back(candidates[idx]);
            vector<vector<int>> ans = solve(candidates, target - candidates[idx]*(idx - i + 1), x);
            
            for (auto vec: ans) {
                vec.insert(vec.end(), v.begin(), v.end());
                res.push_back(vec);
            }
        }

        vector<vector<int>> ans = solve(candidates, target, x);
        res.insert(res.end(), ans.begin(), ans.end());

        return res;
    }
public:
    vector<vector<int>> combinationSum2(vector<int>& candidates, int target) {
        sort(candidates.begin(), candidates.end());

        return solve(candidates, target, candidates.size() - 1);
    }
};
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