39. Combination Sum

Given a set of candidate numbers (candidates) (without duplicates) and a target number (target), find all unique combinations in candidates where the candidate numbers sums to target.

The same repeated number may be chosen from candidates unlimited number of times.

Note:

• All numbers (including target) will be positive integers.
• The solution set must not contain duplicate combinations. Example 1:

Input: candidates = [2,3,6,7], target = 7,
A solution set is:
[
  [7],
  [2,2,3]
]

Example 2:

Input: candidates = [2,3,5], target = 8,
A solution set is:
[
  [2,2,2,2],
  [2,3,3],
  [3,5]
]

Solution

Approach 1: DFS.

Code (Python)

Approach 1:

Code (C++)

Approach 1:

class Solution {
private:
    vector<vector<int>> solutionSet;
    void combinationSum(vector<int>& candidates, int head, int target, vector<int>& solution) {
        if (target == 0)
        {
            solutionSet.push_back(solution);
            return;
        }
        for (int i = head; i < candidates.size(); ++i)
        {
            if (candidates[i] > target)
                break;
            solution.push_back(candidates[i]);
            combinationSum(candidates, i, target - candidates[i], solution);
            solution.pop_back();
        }
    }
public:
    vector<vector<int>> combinationSum(vector<int>& candidates, int target) {
        vector<int> solution;
        std::sort(candidates.begin(), candidates.end());
        combinationSum(candidates, 0, target, solution);
        return solutionSet;
    }
};