Combination Sum III

1. Title

Combination Sum III

2. Http address

https://leetcode.com/problems/combination-sum-iii/

3. The question

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.

Ensure that numbers within the set are sorted in ascending order.

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]]

4. My code(AC)

    // Accepted
      public List<List<Integer>> combinationSum3(int k, int n) {
            
          List<List<Integer>> result = new ArrayList<List<Integer>>();
          getNumber(1, k , n, new ArrayList<Integer>(), result);
          return result;
        }
      
      public void getNumber(int begin, int k , int n, ArrayList<Integer> subList, List<List<Integer>> result)
      {
        int len = subList.size();
        int sum = 0;
        if( len == k )
        {
            for(int i = 0 ; i < len ; i++)
            {
                sum += subList.get(i);
            }
            if( sum == n)
            {
                result.add(new ArrayList<Integer>(subList));
            }
            return;
        }
        
        for(int i = begin ; i <= 9 ; i++)
        {
            subList.add(i);
            getNumber(i + 1, k, n, subList, result);
            subList.remove(subList.size() - 1);
        }
      }