标签：less rip ret java 个数 solution ++ positive algo
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:
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] ]
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<List<Integer>> combinationSum2(int[] candidates, int target) 4 { 5 List<List<Integer>> 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<Integer>> list, List<Integer> 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 greater 16 return false; // therefore, no need to continue the loop, return false 17 else if(remain == 0) 18 { 19 list.add(new ArrayList<>(tempList)); 20 return false; 21 } 22 else 23 { 24 for(int i=start; i<nums.length; i++) 25 { 26 if(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 continue 34 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 sum 38 } 39 40 } 41 }
参考资料：
http://www.cnblogs.com/grandyang/p/4419386.html
LeetCode 算法题目列表 - LeetCode Algorithms Questions List
LeetCode 40. Combination Sum II （组合的和之二）
标签：less rip ret java 个数 solution ++ positive algo
原文地址：http://www.cnblogs.com/jimmycheng/p/7198400.html
