216_Combination_Sum_III.java

classSolution {
publicList<List<Integer>> combinationSum3(intk, intn) {
List<List<Integer>> result = newArrayList<>();
helper(n, k, 1, newArrayList<>(), result);
returnresult;
 }

privatevoidhelper(intn, intnumsAllowed, intstart, List<Integer> temp, List<List<Integer>> result) {
if (numsAllowed == 0 && n == 0) {
result.add(newArrayList<>(temp));
return;
 }

for (inti = start; i <= 9; i++) {
temp.add(i);
helper(n - i, numsAllowed - 1, i + 1, temp, result);
temp.remove(temp.size() - 1);
 }
 }
}