LeetCode Q39: Combination Sum

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.
• Elements in a combination (a1, a2, … , ak) must be in non-descending order. (ie, a1 ≤ a2 ≤ … ≤ ak).
• 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] 

Solution:

Use recursive, every iteration, choose to add current number or jump to next number.

	class Solution {
	public:
	void helper(vector<vector<int> >& res, vector<int>& candidates, int target, int idx, vector<int>& cur, int sum){
	if(sum == target){
	res.push_back(cur);
	return;
	}
	if(sum>target)
	return;
	cur.push_back(candidates[idx]);
	helper(res, candidates, target, idx, cur, sum+candidates[idx]);
	cur.pop_back();
	if(idx+1<candidates.size())
	helper(res, candidates, target, idx+1, cur, sum);
	}
	vector<vector<int>> combinationSum(vector<int>& candidates, int target) {
	vector<vector<int> > res;
	if(candidates.empty())
	return res;
	sort(candidates.begin(), candidates.end());
	vector<int> cur;
	helper(res, candidates, target, 0, cur, 0);
	return res;
	}
	};

view raw Q39.cpp hosted with ❤ by GitHub