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 List<List<Integer>> combinationSum3(int k, int n) {
List<List<Integer>> result = new ArrayList<>();
backtrack(k, n, result, new ArrayList<Integer>(), 1, 0);
return result;
}
public void backtrack(int k, int n, List<List<Integer>> result, ArrayList<Integer> temp, int curr, int sum) {
if(temp.size() > k) return;
if(sum >= n) {
if(sum == n && temp.size() == k) result.add(new ArrayList<>(temp));
return;
}
for(int i = curr; i < 10; i++) {
temp.add(i);
backtrack(k, n, result, temp, i+1, sum+i);
temp.remove(temp.size()-1);
}
}