Combination Sum III

arraybacktracking

Problem Statement

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.

Examples

Example 1

Input: k = 3, n = 7
Output: [[1,2,4]]
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]]
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: []
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.

Constraints

2 <= k <= 9

1 <= n <= 60

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Medium

Difficulty

Topic Info

ModuleDSA

CategoryArray

Sub-topicBacktracking