[LeetCode-Algorithms-39] "Combination Sum" (2017.11.29-WEEK13)

题目链接：Combination Sum

• 题目描述：
  

Given a set of candidate numbers (C) (without duplicates) 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]]

---

(1)思路：使用深度优先的方法搜索，并且用一个vector记录向量，找到合适的向量时将它保存在结果中并进行回溯操作。

(2)代码：

class Solution {public:   vector<vector<int> > combinationSum(vector<int>& candidates, int target) {        vector<vector<int> > result;        vector<int> path;        sort(candidates.begin(),candidates.end());        helper(candidates,0,0,target,path,result);        return result;    }    void helper(vector<int> &nums,int pos,int base,int target,vector<int>& path,vector<vector<int> > & result)    {        if(base==target)        {            result.push_back(path);            return ;        }        if(base>target)            return ;        for(int i=pos;i<nums.size();i++)        {            path.push_back(nums[i]);            helper(nums,i,base+nums[i],target,path,result);            path.pop_back();        }    }};

(3)提交结果：