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.

Example 1:

Input: candidates = [10,1,2,7,6,1,5], target = 8
Output: 
[
[1,1,6],
[1,2,5],
[1,7],
[2,6]
]

Example 2:

Input: candidates = [2,5,2,1,2], target = 5
Output: 
[
[1,2,2],
[5]
]

Constraints:

• 1 <= candidates.length <= 100

• 1 <= candidates[i] <= 50

• 1 <= target <= 30

Solution:

class Solution:
    def combinationSum2(self, candidates: List[int], target: int) -> List[List[int]]:
        candidates.sort()

        res = []

        def backtrack(cur, pos, target):
            if target == 0:
                res.append(cur.copy())
                return
            if target <= 0:
                return

            prev = -1
            for i in range(pos, len(candidates)):
                if candidates[i] == prev:
                    continue
                cur.append(candidates[i])
                backtrack(cur, i + 1, target - candidates[i])
                cur.pop()
                prev = candidates[i]

        backtrack([], 0, target)
        return res