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]]

 

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题目标签：Array

　　这道题目和前面那一题本质一摸一样，不同之处是，这题每一个数字只能用一次，之前那题可以无限用；这一题给的array里有重复的，之前那题没有。所以只要之前那题做了，稍微改动一下就可以了。把递归下去的数字index 从i 改成 i + 1，因为这里不需要重复的数字了。再有就是要设一个条件，如果一个重复的数字，不是出现在第一位的话，就跳过它。

 

 

Java Solution:

Runtime beats 83.86% 

完成日期：07/17/2017

关键词：Array

关键点：Backtracking with sorted array

 

1 public class Solution  2 { 3     public List
      
       
        > combinationSum2(int[] candidates, int target)  4     { 5         List
        
         
          > list = new ArrayList<>(); 6         Arrays.sort(candidates); 7         backtrack(list, new ArrayList<>(), candidates, target, 0); 8          9         return list;10     }11     12     public boolean backtrack(List
          
           
            > list, List
            
              tempList, 13 int[] nums, int remain, int start)14 {15 if(remain < 0) // if remain is 0 or less than 0, meaning the rest numbers are even greater16 return false; // therefore, no need to continue the loop, return false17 else if(remain == 0)18 {19 list.add(new ArrayList<>(tempList));20 return false;21 }22 else23 {24 for(int i=start; i
             
               start && nums[i] == nums[i-1])27 continue;28 boolean flag;29 tempList.add(nums[i]);30 flag = backtrack(list, tempList, nums, remain - nums[i], i+1); // i + 1 because we cannot use same number.31 tempList.remove(tempList.size() - 1);32 33 if(!flag) // if find a sum or fail to find a sum, there is no need to continue34 break;// because it is a sorted array with no duplicates, the rest numbers are even greater.35 }36 37 return true; // return true because previous tempList didn't find a sum or fail a sum38 }39 40 }41 }
             
            
           
          
         
        
       
      

参考资料：

http://www.cnblogs.com/grandyang/p/4419386.html

 

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