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Java Solution for LeetCode algorithm problems, continually updating
39\. Combination Sum
Medium
Given an array of **distinct** integers `candidates` and a target integer `target`, return _a list of all **unique combinations** of_ `candidates` _where the chosen numbers sum to_ `target`_._ You may return the combinations in **any order**.
The **same** number may be chosen from `candidates` an **unlimited number of times**. Two combinations are unique if the frequency of at least one of the chosen numbers is different.
It is **guaranteed** that the number of unique combinations that sum up to `target` is less than `150` combinations for the given input.
**Example 1:**
**Input:** candidates = [2,3,6,7], target = 7
**Output:** [[2,2,3],[7]]
**Explanation:**
2 and 3 are candidates, and 2 + 2 + 3 = 7. Note that 2 can be used multiple times.
7 is a candidate, and 7 = 7.
These are the only two combinations.
**Example 2:**
**Input:** candidates = [2,3,5], target = 8
**Output:** [[2,2,2,2],[2,3,3],[3,5]]
**Example 3:**
**Input:** candidates = [2], target = 1
**Output:** []
**Example 4:**
**Input:** candidates = [1], target = 1
**Output:** [[1]]
**Example 5:**
**Input:** candidates = [1], target = 2
**Output:** [[1,1]]
**Constraints:**
* `1 <= candidates.length <= 30`
* `1 <= candidates[i] <= 200`
* All elements of `candidates` are **distinct**.
* `1 <= target <= 500`