39. 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]

 

用map来记录一个组合是否出现过。

注意记录cur的vector是值传递，而不是引用。

注意for循环中candidates[i] <= target

class Solution {
public:
void Helper(vector<vector<int>> &ret,vector<int> cur,vector<int> &candidates,int target,map<vector<int>,bool> &m)
{
if(target == 0)
{
sort(cur.begin(),cur.end());
if(m[cur] == false)
{
ret.push_back(cur);
m[cur] = true;
}
}
else
{
for(int i = 0;i<candidates.size() && candidates[i] <= target;i++)
{
int val = candidates[i];
cur.push_back(val);
Helper(ret,cur,candidates,target-val,m);
cur.pop_back();
}
}
}

vector<vector<int> > combinationSum(vector<int> &candidates, int target) {
sort(candidates.begin(),candidates.end());
vector<vector<int>> ret;
map<vector<int>,bool> m;
vector<int> cur;
Helper(ret,cur,candidates,target,m);
return ret;

}
};