combination_sum_2.py

"""
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

"""

class Solution:
    def combinationSum2(self, candidates: List[int], target: int) -> List[List[int]]:
        def dfs(index, current_sum):
            if current_sum == target:
                ans.append(sol.copy())
                return
            if current_sum > target:
                return
            
            for i in range(index, len(candidates)):
                if i > index and candidates[i] == candidates[i-1]:
                    continue
                c = candidates[i]
                sol.append(c)
                dfs(i + 1, current_sum + c)
                sol.pop()
        
        sol = []
        ans = []
        candidates.sort()
        dfs(0,0)
        return ans