Combination Sum III

Find all valid combinations of k numbers from 1 to 9 that sum to n. Each combination is a list of k unique numbers in ascending order.

Examples
Input: [3,7]
Output: [[1,2,4]]
Hints

Combination Sum III

Find all valid combinations of k numbers from 1 to 9 that sum to n. Each combination is a list of k unique numbers in ascending order.