Leetcode 40. Combination Sum II

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

Each number in C 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.

For example, given candidate set [10, 1, 2, 7, 6, 1, 5] and target 8,
A solution set is:

[
  [1, 7],
  [1, 2, 5],
  [2, 6],
  [1, 1, 6]
]

 

这道题和Leetcode 39差不多，区别是一个元素只能用一次，所以L27里面用了candidates[i+1:]。另外需要注意的是，[1a,2,5] 和 [1b,2,5]在结果中应被视为重复解而去掉一个。所以用了L13-L16。

 class Solution(object):
     def combinationSum2(self, candidates, target):
         """
         :type candidates: List[int]
         :type target: int
         :rtype: List[List[int]]
         """
         candidates.sort()
 
         res = []
         self.helper(candidates, target, res, [])
 
         ans = []
         for elem in res:
             if elem not in ans:
                 ans.append(elem)
 
         return ans
 
     def helper(self, candidates, target, res, line):
         if target == 0:
             res.append([x for x in line])
 
         for i,x in enumerate(candidates):
             if x <= target:
                 line.append(x)
                 self.helper(candidates[i+1:], target - x, res, line)
                 line.pop()