Solution (leetcode-in-java 1.23 API)

java.lang.Object
- g0201_0300.s0216_combination_sum_iii.Solution

```
public class Solution
extends Object
```
216 - Combination Sum III.
Medium

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

Explanation:
```
 1 + 2 + 4 = 7
 There are no other valid combinations.
```
Example 2:

Input: k = 3, n = 9

Output: [[1,2,6],[1,3,5],[2,3,4]]

Explanation:
```
 1 + 2 + 6 = 9
 1 + 3 + 5 = 9
 2 + 3 + 4 = 9
 There are no other valid combinations. 
```
Example 3:

Input: k = 4, n = 1

Output: []

Explanation:
```
 There are no valid combinations.
 Using 4 different numbers in the range [1,9], the smallest sum we can get is 1+2+3+4 = 10 and since 10 > 1, there are no valid combination. 
```
Example 4:

Input: k = 3, n = 2

Output: []

Explanation: There are no valid combinations.

Example 5:

Input: k = 9, n = 45

Output: 1,2,3,4,5,6,7,8,9

Explanation:
```
 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 = 45
 There are no other valid combinations. 
```
Constraints:
- 2 <= k <= 9
- 1 <= n <= 60

- Constructor Summary
  
  Constructors
  Constructor Description
  
  Solution()
- Method Summary
  
  All Methods Instance Methods Concrete Methods
  Modifier and Type Method Description
  
  List<List<Integer>> combinationSum3(int k, int n)
  - Methods inherited from class java.lang.Object
    clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail
- Solution
```
public Solution()
```

Method Detail

combinationSum3

public List<List<Integer>> combinationSum3(int k,
                                           int n)