Leetcode 39. Combination Sum (Medium) (cpp)

Leetcode 39. Combination Sum (Medium) (cpp)

Tag: Array, Backtracking

Difficulty: Medium

/*39. Combination Sum (Medium)Given a set of candidate numbers (C) and a target number (T), find all unique combinations in C where the candidate numbers sums to T.The same repeated number may be chosen from C unlimited number of times.Note:All numbers (including target) will be positive integers.The solution set must not contain duplicate combinations.For example, given candidate set [2, 3, 6, 7] and target 7, A solution set is: [  [7],  [2, 2, 3]]*/class Solution {public:    vector<vector<int>> combinationSum(vector<int>& candidates, int target) {        vector<vector<int>> res;        vector<int> res_sub;        sort(candidates.begin(), candidates.end());        combinationSum(candidates, target, 0, res_sub, res);        return res;    }private:    void combinationSum(vector<int>& candidates, int target, int start, vector<int>& res_sub, vector<vector<int>>& res) {        if (target < 0 || start > candidates.size()) {            return;        } else if (target == 0) {            res.push_back(res_sub);            return;        }        for (int i = start; i < candidates.size() && candidates[i] <= target; i++) {           res_sub.push_back(candidates[i]);           combinationSum(candidates, target - candidates[i], i, res_sub, res);           res_sub.pop_back();       }   }};