Combination Sum

难度：2

- -本来想用背包做，发现用来做这题好麻烦，最后还是DFS裸搜了

个人总结：1Y达成

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] 

class Solution {public:vector<vector<int> >ans;vector<int>tmp;void dfs(int left, int cur_index,vector<int> &candidates){if(left == 0){ans.push_back(tmp);return;}for(int i=cur_index;i<candidates.size();i++){if(left-candidates[i] >= 0){tmp.push_back(candidates[i]);dfs(left-candidates[i],i,candidates);tmp.pop_back();}}}    vector<vector<int> > combinationSum(vector<int> &candidates, int target) {sort(candidates.begin(),candidates.end());candidates.erase(unique(candidates.begin(),candidates.end()),candidates.end());ans.clear();tmp.clear();dfs(target,0,candidates);return ans;    }};