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 {
List<List<Integer>> ans = new ArrayList<>();
List<Integer> currCombination = new ArrayList<>();
public List<List<Integer>> combinationSum3(int k, int n) {
makeCombination(k,n,1);
return ans;
}
public void makeCombination(int k,int n,int start)
{
if(k==0 && n==0)
{
ans.add(new ArrayList<>(currCombination));
return;
}
for(int i=start;i<10;++i)
{
currCombination.add(i);
makeCombination(k-1,n-i,i+1);
currCombination.remove(currCombination.size()-1);
}
}
}
