216. Combination Sum III

题目

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.

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]]

Credits:Special thanks to @mithmatt for adding this problem and creating all test cases.

解题思路

常见的dfs搜索，见程序注释