Combination Sum

Given a set of candidate numbers (C) and a target number (T), find all unique combinations in C where the candidate numbers sums to T. The same repeated number may be chosen from C unlimited number of times.

 Note: All numbers (including target) will be positive integers.
Elements in a combination (a1, a2, ... , ak) must be in non-descending order. (ie, a1 < a2 < ... < ak).
The solution set must not contain duplicate combinations.

For example, given candidate set 2,3,6,7 and target 7, A solution set is: [7] [2, 2, 3]

Solution: recursive version without sorting and set. Sorting it first and use set for avoiding duplicates DP (pass large judge)

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