Given a collection of candidate numbers (candidates) and a target number (target), find all unique combinations in candidates where the candidate numbers sums to target.
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Use backtracking, sort input, and save index of number used. Pick one number at a time to fill temp array, that is not same as previous in array. Once temp array sum is target, add it to result. Each time choose next number, and check if it was used with set. O(n!) time, O(n) space.Run make to run python and Swift files.