Problem: Combination Sum

Statement

Given an array of distinct integers candidates and a target integer target, return all unique combinations of numbers from candidates that sum up to target. The combinations may be returned in any order.

Each number in candidates may be selected an unlimited number of times. Two combinations are considered unique if they differ in the frequency of at least one chosen number.

Constraints:

• $1 \leq$ candidates.length $\leq 30$

• $2 \leq$ candidates[i] $\leq 40$

• All elements of candidates are distinct.

• $1 \leq$ target $\leq 40$ ...