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]
]


考察要点: 基本的DFS, 其他没有难度, 注意数组的元素可以被重复利用

class Solution {
public:
    vector<vector<int>> combinationSum(vector<int>& candidates, int target) {
        sort(candidates.begin(),candidates.end());
        vector<vector<int>> res;
        vector<int> candi;
        traverse(candidates,target,res,candi,0);
        return res;
    }

    void traverse(vector<int> &candidates,int target, vector<vector<int>> &res, vector<int> &cur, int index)
    {
        if(0==target)
        {
            res.push_back(cur);
            return;
        }

        for(;index<candidates.size()&&target>=candidates[index];++index)
        {
            cur.push_back(candidates[index]);
            traverse(candidates,target-candidates[index],res,cur,index);
            cur.pop_back();
        }
    }
};