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 toT.

Each number in C may only be used once in the combination.

Note:

• All numbers (including target) will be positive integers.
• Elements in a combination (a1, a2, … , ak) must be in non-descending order. (ie, a1 ≤ a2 ≤ … ≤ ak).
• 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] 

思路：和Combination Sum 基本一致，主要不同是不允许一个元素多次被使用。

JAVA代码：

1. ArrayList<ArrayList<Integer> > res = new ArrayList<ArrayList<Integer>>();
2. ArrayList<Integer> cur = new ArrayList<Integer>();
3. void helper(int[] num,int target,int start) {
4. if( start==num.length || target<=0) {
5. if(target==0)
6. res.add(new ArrayList<Integer>(cur));
7. return;
8. }
9. for(int i=start;i<num.length;i++) {
10. if(i > start && num[i] == num[i-1]) {
11. continue;
12. }
13. cur.add(num[i]);
14. helper(num,target-num[i],i+1);
15. cur.remove(cur.size()-1);
16. }
17. }
18. public ArrayList<ArrayList<Integer>> combinationSum2(int[] num, int target) {
19. if(num==null) return res;
20. Arrays.sort(num);
21. helper(num,target,0);
22. return res;
23. }