Combination Sum II

题目

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 target8,
A solution set is:

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

思路分析

这道题跟combination sum那道题很类似，但是有两个重要的不同：

• Combination Sum I求和的时候可以重复利用数组中的数字，而Combination Sum II要求每一个数字只能用一次

• Combination Sum I给的数组中没有重复的数字，而Combination Sum II给的数组中有重复的数字，所以在实现Combination Sum II的时候要考虑结果去重的问题:

   **if i>startIndex and candidates\[i\]==candidates\[i-1\]: continue**
  

class Solution(object):
    def combinationSum2(self, candidates, target):
        """
        :type candidates: List[int]
        :type target: int
        :rtype: List[List[int]]
        """
        def dfs(candidates, target, startIndex, path, result):
            if target < 0: return
            if target == 0:
                result.append(path)
                return
            for i in range(startIndex, len(candidates)):
                if candidates[i] > target: return
                if i>startIndex and candidates[i]==candidates[i-1]: continue
                dfs(candidates, target-candidates[i], i+1, path+[candidates[i]], result)
        result = []
        dfs(sorted(candidates), target, 0, [], result)
        return result