Combination Sum

Given an array of candidate numbers A and a target number B, find all unique combinations in A where the candidate numbers sums to B.

The same repeated number may be chosen from A unlimited number of times.

Note:

1) All numbers (including target) will be positive integers.

2) Elements in a combination (a1, a2, … , ak) must be in non-descending order. (ie, a1 ≤ a2 ≤ … ≤ ak).

3) The combinations themselves must be sorted in ascending order.

4) CombinationA > CombinationB iff (a1 > b1) OR (a1 = b1 AND a2 > b2) OR ... (a1 = b1 AND a2 = b2 AND ... ai = bi AND ai+1 > bi+1)

5) The solution set must not contain duplicate combinations.

1 <= |A| <= 20

1 <= A[i] <= 50

1 <= B <= 500

The first argument is an integer array A.

The second argument is integer B.

Return a vector of all combinations that sum up to B.

Input 1:

A = [2, 3]
B = 2

Input 2:

A = [2, 3, 6, 7]
B = 7

Output 1:

[ [2] ]

Output 2:

[ [2, 2, 3] , [7] ]

Explanation 1:

All possible combinations are listed.

Explanation 2:

All possible combinations are listed.