39.Combination Sum

Tags: Medium Backtracking Array

Links: https://leetcode.com/problems/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]
]

---

class Solution {
    void DFS(vector<int>& candidates, int gap, int startPosition, vector<int> &tmp, vector<vector<int>> &result)
    {
        if (gap == 0){
            result.push_back(tmp);
            return;
        }

        for (size_t i = startPosition; i < candidates.size(); ++i){
            if (gap < candidates[i]) return;

            tmp.push_back(candidates[i]);
            DFS(candidates, gap - candidates[i], i, tmp, result);
            tmp.pop_back();
        }
    }

public:
    vector<vector<int>> combinationSum(vector<int>& candidates, int target) {
        vector<vector<int>> result;
        vector<int> tmp;

        sort(candidates.begin(), candidates.end());

        DFS(candidates, target, 0, tmp, result);

        return result;
    }
};