LeetCode 216. Combination Sum III

递归即可。

代码：

class Solution
{
public:
vector<vector<int>> combinationSum3(int k, int n)
{
for (int i = 1; i<=9 && k>0 && i<=n; ++ i)
{
vector<int> cur(1, i);
gao(i+1, k-1, n-i, cur);
}
return ret;
}

private:
void gao(int begin, int k, int n, vector<int>& cur)
{
if (k==0 && n==0)
{
ret.push_back(cur);
return;
}
for (int i = begin; i<=9 && k>0 && i<=n; ++ i)
{
cur.push_back(i);
gao(i+1, k-1, n-i, tmp);
cur.pop_back();
}
}

vector<vector<int>> ret;
};