/**
* Find all possible combinations of k numbers that add up to a number n, given
* that only numbers from 1 to 9 can be used and each combination should be a
* unique set of numbers.
*
* Note:
* All numbers will be positive integers.
* The solution set must not contain duplicate combinations.
*
* Example 1:
* Input: k = 3, n = 7
* Output: [[1,2,4]]
*
* Example 2:
* Input: k = 3, n = 9
* Output: [[1,2,6], [1,3,5], [2,3,4]]
*/
public class CombinationSumIII216 {
public List> combinationSum3(int k, int n) {
List
> res = new ArrayList<>();
combinationSum3(k, n, new boolean[9], new ArrayList<>(), 0, 1, res);
return res;
}
private void combinationSum3(int k, int n, List
> res) {
if (path.size() == k) {
if (sum == n) res.add(new ArrayList<>(path));
return;
}
for (int i=start; i<=9; i++) {
path.add(i);
combinationSum3(k, n, visited, path, sum + i, i+1, res);
path.remove(path.size()-1);
}
}
}