# Question

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.

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

Note:

All numbers (including target) will be positive integers. The solution set must not contain duplicate combinations.

Example 1:

Input: candidates = [10,1,2,7,6,1,5], target = 8,
A solution set is:
[
[1, 7],
[1, 2, 5],
[2, 6],
[1, 1, 6]
]


Example 2:

Input: candidates = [2,5,2,1,2], target = 5,
A solution set is:
[
[1,2,2],

]


# Solution

Use backtracking. Because candidates can contain duplicate numbers, use a set to dedupe results.

class Solution:
def combinationSum2(self, candidates, target):
"""
:type candidates: List[int]
:type target: int
:rtype: List[List[int]]
"""
solutions = set()
progress = list()
candidates.sort()

def backtracking(candidates, target, solutions, progress, current_sum, last_index):
if current_sum == target:
progress = list()
else:
diff = target - current_sum
for idx in range(last_index + 1, len(candidates)):
if candidates[idx] <= diff:
progress.append(candidates[idx])
backtracking(candidates, target, solutions, progress, current_sum + candidates[idx], idx)
if len(progress) > 0:
progress.pop()
else:
break

backtracking(candidates, target, solutions, progress, 0, -1)
return list(solutions)