LeetCode 40 Combination Sum II time limit exceeded

Question

I'm working on LeetCode 40. Combination Sum II

Given a collection of candidate numbers (candidates) and a target number (target), find all unique combinations in candidates where the candidate numbers sum to target.

Each number in candidates may only be used once in the combination.

Note: The solution set must not contain duplicate combinations.

My code below works until the candidates collection gets too big, then I get back "time limit exceeded". All of the recursion is creating too many loops I think. I can obviously copy tutorials to get the answer but I'm trying to figure out how my code could be updated to work in order to understand better how recursion works.

class Solution:
    def combinationSum2(self, candidates: List[int], target: int) -> List[List[int]]:
        candidates.sort()
        answers = []
        strings = []
        total = sum(candidates)
        if total < target:
            return []
        def backtrack(total, array, index):
            if total == 0:
                string = ''
                for each in array:
                    string += str(each)
                if string not in strings:
                    answers.append(array)
                    strings.append(string)
                    return
            if index >= len(candidates):
                return
            for each in range(index, len(candidates)):
                backtrack(total - candidates[each], array + [candidates[each]], each + 1)
                backtrack(total, array, each + 1)
        backtrack(target, [], 0)
        return answers

Answer 1

It is a good idea to sort the candidates, but you do not use it. You should recuser only if total-candidate[i]>0, break if <0 and return if =0