[Leetcode] 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.
• 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] 

Solution:

public class Solution {
    public List<List<Integer>> combinationSum2(int[] candidates, int target) {
        List<List<Integer>> result=new ArrayList<List<Integer>>();
        List<Integer> al=new ArrayList<Integer>();
        Arrays.sort(candidates);
        dfs(result,al,target,candidates,0);
        return result;
    }

    private void dfs(List<List<Integer>> result, List<Integer> al, int target, int[] candidates, int position) {
        // TODO Auto-generated method stub
        if(target<0)
            return;
        if(target==0){
            result.add(new ArrayList<Integer>(al));
            return;
        }
        for(int i=position;i<candidates.length;++i){
            al.add(candidates[i]);
            dfs(result, al, target-candidates[i], candidates, i+1);
            al.remove(al.size()-1);
            while((i+1<candidates.length)&&candidates[i]==candidates[i+1])
                ++i;
        }    
    }
}

这道题和Combination Sum那道题很像，区别就是在第20行和第22行，

如果candidates[i]==candidates[i+1]，就直接跳过candidates[i+1]这个选项了，因为不能有重复的solution嘛。