<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>

#include <vector>
#include <set>
#include <unordered_map>
#include <algorithm>

class Solution {
public:
    int n;
    std::set<std::vector<int>> st; // To store unique combinations

    void find(int ind, std::vector<int>& candidates, int t, std::unordered_map<int, int>& mp, std::vector<int>& temp) {
        if (t == 0) {
            // Add the combination to the set if it meets the target
            st.insert(temp);
            return;
        }
        if (ind >= n || t < 0) {
            return;
        }

        // Include the current element only if it's valid
        int currentNum = candidates[ind];
        int maxCount = mp[currentNum];
        
        for (int i = 0; i <= maxCount; ++i) {
            // Try to use 'i' occurrences of the current number
            if (t - currentNum * i >= 0) {
                std::vector<int> tempCopy = temp;
                tempCopy.insert(tempCopy.end(), i, currentNum);
                find(ind + maxCount , candidates, t - currentNum * i, mp, tempCopy);
            }
        }
    }

    std::vector<std::vector<int>> combinationSum2(std::vector<int>& candidates, int target) {
        n = candidates.size();
        std::sort(candidates.begin(), candidates.end()); // Sort to handle duplicates
        std::unordered_map<int, int> mp;
        for (int i : candidates) mp[i]++;
        std::vector<int> temp;
        find(0, candidates, target, mp, temp);

        // Convert set to vector
        std::vector<std::vector<int>> ans(st.begin(), st.end());
        return ans;
    }
};
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