Leetcode 40. Combinations 2 solution using backtracking

Combinations-2.cpp

class Solution {
private:
    vector<int> combination;
    vector<vector<int>> combinations;
public:
    vector<vector<int>> combinationSum2(vector<int>& candidates, int target) {
        sort(candidates.begin(), candidates.end());
        
        explore(candidates, 0, target);
        return combinations;
    }
    
    void explore(vector<int>& candidates, int start, int target){
        if(target == 0){
            combinations.push_back(combination); 
            return;
        }    
        if(target < 0) return; 

        for(int i = start; i < candidates.size(); i++){
            if(i > start && candidates[i] == candidates[i-1]) continue; // skip duplicates
            
            // explore all solutions using candidates[i] exactly once
            combination.push_back(candidates[i]);
            explore(candidates, i+1, target - candidates[i]);
            
            // explore solutions that don't use candidates[i]
            combination.pop_back();
        }
    }
};