2. Implement a backtracking algorithm.

Given a collection of amount values (A) and a target sum (S), find all unique combinations in A where the amount values sum up to S.

Each amount value may be used only once in the combination.

The solution set should not contain duplicate combinations.

Amounts will be positive numbers.

Example: A = [11,1,3,2,6,1,5]; Target Sum = 8

Result = [3, 5]

[2, 6]

[1, 2, 5]

[1, 1, 6]

What is the time complexity of your implementation, you may find time complexity in detailed or state whether it is linear/polynomial/exponential. etc.?