Find all valid combinations of k numbers that sum up to n such that the following conditions are true:
Only numbers 1 through 9 are used. Each number is used at most once.
Return a list of all possible valid combinations. The list must not contain the same combination twice, and the combinations may be returned in any order.
Example 1:
Input: k = 3, n = 7
Output: [[1,2,4]]
class Solution {
public:
vector<vector<int>> ans;
vector<int> currCombination;
vector<vector<int>> combinationSum3(int k, int n) {
makeCombination(k,n,1);
return ans;
}
void makeCombination(int k,int n,int start){
if(k==0 && n==0)
{
ans.push_back(currCombination);
return;
}
for(int i = start;i<10;++i)
{
currCombination.push_back(i);
makeCombination(k-1,n-i,i+1);
currCombination.pop_back();
}
}
};
